I use a lot of the Saddle Panniers that you just throw over a riding saddle. No you can't carry as much as a good decker saddle. But they work. Having 3 daughters who often went with me and not wanting to take 6-7 horses, We often packed two horses, I would lead and my daughters hike. Once camp was set up, we still had enough horses with riding saddles for us to take day ride out and back from the camp site. I also use the same paniers when I'm elk and deer hunting, they roll up and we tie them behind the cantle. Ride all day for the hunt, when we harvest something, We load it into the panniers and lead the horse back to camp or the truck.
Not suggesting this is the only way to go. But panniers do offer some versitility vs a dedicated pack saddle. Plus they are only a $100.
I've never had much trouble teaching any of the horses to be a pack horse. Put the saddle on, throw the pannier over the top and drop in a couple of salt blocks and haul them up and place them for the deer and elk, or put my chain saw, some fuel and gear in the opposite side and go clear dead falls off the spring trails. Horse gets used to the packs and the chain saw noise during the same trip and the trail riders the rest of the summer say thanks for the cleared trails. If you have horse that cuts too close to trees, tie a couple of old tires on the saddle and let him bang into trees with the tires. They learn real quick to go wide.
My daughter with a pack horse using panniers
As much as I hate to admit this bad habit. I do frequently just turn my pack horse loose and let it follow on it own. The personality of the horse will determine if this is acceptable for you. You don't want horses that fight and kick to maintain position along the trail, nor do I want to chase after a loose horse. But my horses started tagging along with me on rides when they were just babies and they 've learned to follow the leader down the trail. Having a horse that will stay in formation with out a lead rope, has it's advantages when the going gets rough and I need to give more spacing to deal with obsticles.
You can see a couple of yearlings following my daughters on this ride. They just run alongside like a hound dog, sniffing and checking things out, but in general staying close to moma. But in the end they learn to follow the leader.
Regardless of what style pack you choose. Having an extra horse along to will allow you to enjoy your trip more. You can take more food, better creature comforts for you, and not feel so overloaded on your riding horse. We easily get by with 1 pack horse for two campers and often do it with a 3:1 ratio. Have Fun