dressage and western riding are kisssing cousins
I think it is much easier for western riders to learn dressage than it is for them to learn hunt seat (english). Dressage and Western riding have more in common than with hunt seat . Both utilize a seat which is IN the horse rather than ON the horse. I mean that hunt seat asks the rider to balance lightly over the horse in preperation for jumps or sudden changes like riding cross country.
Western and Dressage want the rider more deeply seated "into " the horse with more emphasis on collection and precise movement and communication between rider and horse. Not that hunt seat doesn't have that too, but it IS different.
Anyway, you will find the dressage saddle much more secure feeling than a typical english saddle; closer to a W saddle. In correct W riding you have a long leg and use a lot of seat aids to ride. Same in dressage.
Now if you are one of the W riders who brace into the stirrups and have a really hard chair seat, then you will have to make some radical changes in the way you sit the horse and rely on balance, not brace.
The other thing that is hard for W riders is the need to have some contact with the horse's mouth. This can be hard for W riders to accept but it will be essential to allow yourself to take up the reins and feel the horse's mouth.
And another thing is that you will need to have more impulsion from your horse. The W jog will not work for dressage. YOu have to be ready to ask the horse to really move out and go forward.
Does that sound interesting to you?