This is an extreme measure and maybe not the answer for most but taking up jiu jitsu is 100% beneficial to your pool game, and not just in the physical well being aspect, it’s also a mental game the same as pool. I’ve been doing it for years now and tho pool had nothing to do with why I started, it absolutely changes everything. It enhances your mobility but also changes the way you look at the game. Hesitation is less, panic is less and you worry less. I’ve also heard yoga is good for pool, which I have yet to try but plan to.
Yesrs ago while at the Mr Olympia a friend of mine introduced me to a company called Sweet Sweat, they’re much bigger today than back then. He was friends with the owner and at the time they were one of the first companies selling the neoprene belts you wear around your abdomen. So many products are a gaff these days but that one is legit and is the simplest thing to do. You can wear it while playing and tho it’s not a back support item, it does help with that also.