I suggest that doing anything is better than wondering if it's a max capacity or not. Trainers are helpful if you need the motivation or structure, but only you really know what your capacity is by listening to your body during the exercises. There are a lot of trainers who will simply tell you what to do and give you structure/make exercise more dynamic, but that doesn't mean they know what your max effort is. When you can't do anymore because you're winded or your muscles are burning... that's your answer... and if you keep pushing to that level, your body will tune up to meet the challenge and raise the bar.

I think the aquatics approach is a great idea if you have access to a pool for laps and can use weights underwater in the shallow end. Some of my best exercise memories when I was younger was swinging a baseball bat underwater and doing all sorts of rotational movements against the resistance of the water. There's partial body weightlessness in the pool, but weights underwater are harder to move, which is great to avoid some pain.

So many exercises can be done in a seated position, or with feet off the ground... you got this. Just need to start with something tomorrow and keep at it.