I'm not a dressage rider, but I have made a switch from learning the forward seat in an Aussie saddle to western. I'm not going to recommend anything, actually, but give some things you might want to think about.
Knees gripping. When the forward seat was developed, it had two schools of thought. The Italian school (Santini) taught the knee was a fixed point that should never move.The thigh should rotate around it. The American School (Chamberlin & Littauer) taught a mobile knee - that weight should flow past the knee without interruption (grip) and thus enter the heel. Notice the last paragraph in this quote from Common Sense Horsemanship:
It seemed to me in 1933, when this book appeared (and I haven't changed my mind since), that if the rider's position depended primarily on firmly fixed knees then he was greatly hampered in the use of his legs. For, as long as a strong use of the legs releases the wedging of the knees, it would seem that the rider's position would be weakened every time he had to control the horse forcibly. Of course, on perfectly schooled horses, such moments may occur very rarely and don't have to be considered seriously; but a perfectly schooled horse is far from being a general case in this world, at least today.
I am also against gripping strongly with knees alone because as a result of abrupt movements of the horse which the rider has not been able to follow rhythmically he often loses his position by pivoting on the knees, usually landing on the horse's neck or beyond. All of us have seen this happen to such riders during unexpected refusals or irregular take-offs for the jump. Obviously, gripping with the lower thighs, knees and upper calves is stronger than with the knees alone.
Furthermore, a strongly fixed knee interferes with the flow of the weight into the stirrups and stiffens the knee joints, thus greatly diminishing the amount of spring in the rider's body. This spring, which is rarely mentioned by other schools of forward riding is to me a very important element in a good, effortless forward seat.
And last, but not least,
I am quite certain that a hard grip stiffens a beginner and, once in the habit of being stiff, some never relax in their lives. So how am I to produce relaxed riders (not merely sitters) if my teaching from the outset is to be based on a fixed knee? Thus, with great regret, I had to reject for my work this part of the Italian method, of many principles of which I personally am so fond.
Common Sense Horsemanship, VS Littauer, Chapter 5
"
What do you do when you can't just RELAX?...HOW can I relax so I stop gripping with my knees, pivoting around them..."
It may take a conscious effort to pry your knees apart, particularly at two point. Maybe remove any knee blocks to make it harder to effectively grip with the knee, so you
have to gain security in the stirrup. But that leads to:
Seat-centric vs Stirrup-centric. The Forward Seat, at least as taught originally, was a stirrup-centric approach. As much weight as possible was carried in the stirrup and as little as possible in the seat. Security in riding came from the lower leg, not the seat.
A typical western approach - not universal, but common - is a seat-centric approach. Talking to long time western riders, I've hear things like "
The stirrup is there to keep the toe from falling" and "
My mom told me to pretend there was a raw egg between my foot and the stirrup". [Loved that comment from a woman - very easy for me to visualize!] That is how most of my family has learned to ride, with weight in the seat and almost none in the stirrup.
Coming from a forward seat, and having learned on a very spooky horse, I think security = weight in stirrups. That might be true for jumping, but I've watched my family when their horse spooks, and a seat-centric approach is fine for staying in the saddle.
Riding trails western, I now tend to go back and forth. For most slow riding, I try for weight carried by my seat and my stirrups are toe-rests. That feels good to me at a canter, too. But when things get dicey or for trotting, I prefer my rump slightly out of the saddle with weight flowing past my knees into my heels.
The point being I needed to make a conscious effort to let my weight go into my seat. Or not. And anytime my horse gets more forward or things get tense, I automatically get weight into my stirrups. And yes, I sometimes get tense and nervous even when my horse is relaxed. Learning to ride on a mare who spooked a lot left a mark on me.
Forward or central balance. The goal of a forward seat is to unite the center of gravity of the horse and rider by
the rider moving his weight FORWARD over his horse's natural center of gravity. The goal of collection is to
teach the horse to shift his balance BACK so it will be underneath his rider's. Ideally, the rider should shift in degrees between both, depending on his horse and what he is doing at the time. To me, at least, it always feels more comfortable when my balance is aligned with my horse's.
But if a horse isn't prepared to sustain collection, and I've trained myself to keep my balance with his, then his forward balance will pull mine forward - because that is "comfortable". When my horse is doing a tight turn, it feels good to me to have my weight back - because it is matching what my horse is doing during the turn. When he straightens out and goes forward, my weight tends to follow him.
I don't ride or train in dressage, but it seems like dressage would require a rider to NOT follow his horse forward.
After all, how can the horse learn to shift his balance to meet ours if we always shift ours to meet his? Speaking theoretically, but wouldn't dressage require a rider to keep his balance "behind the horse" at times in order to
teach the horse to rebalance?
A cardinal sin in forward riding is to be behind your horse. But how does one teach a horse to shift his weight back to meet ours if ours is never back to begin with?
In any case...having focused in learning to move my weight to match my horse's balance, I tend to do so regardless. And if my horse gets more forward, it takes a conscious effort for me to refuse to follow him, and to insist he start moving his balance to match mine.
As a trail rider, that isn't a big deal. I'm generally content to have a forward balance. For what I do, collection isn't a big deal. But collection is obviously a big deal in dressage. I don't think I'd have a big problem using a central balance on a horse already trained to collect. But I'd have a lot of problem trying to TEACH a horse to shift his balance back when my every instinct would be to adjust mine.
Just some thoughts on switching from a stirrup-centric forward seat in an Aussie saddle to a more seat-centric approach in a western one. If it doesn't help your thinking, I apologize and wish you well.
PS - "
my stirrups feel too long in trot, but they feel too short in walk and canter"
I find longer stirrups make it easier to canter while seated. For trotting, my horse moves better if I'm out of the saddle. My stirrup position tends to be a compromise between the two. If I plan to do arena work, which for me includes a lot of trotting, then I shorten my stirrups a notch. If I anticipate a spooky horse, I drop them a hole. Normally, I ride in between. All just FWIW.
