I have a compression fracture and a hernioation, and found that a peddle yak didn't bother me at all. Paddling g a yak for hours would get to me especially if I'm fighting wind and/or current. The down side is weight and more stuff to snag lines on your deck.
There are many makes out there. The cheaper ones are make from cheaper plastic that will breakdown faster in UV light. They get brittle and crack easily. They aren't as flexable in the cold, a concern for those of us up north.
Seats are upgradable on most yaks. You can get them with high backs, low backs, lumbar support,... It's up to you what you are looking for.
I have an older surf to summit GTX seat that is amazing. I put it on my wife's SOT so she's comfy. I have a Hobie seat on my Revo with an air bladder in it. I made a removable backrest for those loooong days on the water.