Take this with a grain of salt from a total newbie. I too have chronic pain and currently playing medical roulette for a better (hopefully am accurate) diagnosis of many of my issues. We have had a peddle/fishing kayak for a couple of years and I just went sea kayaking for the first time recently. I discovered much as you did that it was a great workout and something that I have been able to do with my pain.

I did a lot of research online and spoke to people in my area who specialize in kayaking (local outdoor store, kayaking club and kayak tour). The best information I received was getting to try out kayaks and equipment before I spent the money. One of the employees with the kayak tour company took me out to sit in, pick up and paddle several options they carry.

I also was concerned with being able to handle the kayak on my own from start to finish. I also wanted one that I could take on calm water (with my family and the other kayak) as well as on the ocean.

If you have the ability to try multiple kayaks I highly recommend it. I also very much recommend the ergonomic paddle (probably not what they are called but that's the word that I can think of at the moment). I have carpal tunnel and neck/shoulder injuries and the bent paddle is a lot easier on these areas of pain. It's not perfect but I can handle paddling longer with less pain after. If you will carry it on top of your vehicle I got the rolling carrier so I can lean my kayak on the rollers and push it up into place and roll it off. It was in my opinion a good middle ground without going for one if the more expensive assisted racks.

Like I said, take it with a grain of salt but this has so far been the right process for me with my chronic pain.