Hi op, I just wanted to reach out with some empathy. I was diagnosed with a life changing condition when I was 36. It's so hard! I really think there's a unique shitness to getting really ill in your 30s/40s, which is hard for other people to understand. People who say 'you just need to accept your lot' - okay if I was maybe 15-20 years older it could be a slightly easier pill to swallow, but I'm not surrounded by a peer group going through a similar thing (my condition is also very rare).
I'm now 10 years into the journey and lessons for me have been:
Nutrition and sleep are everything- without these I'm not giving myself the best chance..I don't need to be perfect but 80% is a good balance.
Finding a balance with exercise is key - rip up the rule book and devise what works for you. My honest opinion is that there's always something you can do, be consistent with it 3 x a week, and then just build on it, when it gets boring switch it up or go up a level.
Don't give up - I went to netball and had to leave as I couldn't keep up. But I then discovered a sport called walking netball and its fabulous.
Highly recommend walking pads, I got the Urevo on Amazon and its ace.
Also if you have a Better You gym near you, you can apply for a National Disability card (with a letter from your GP) and the card gives you membership nationwide for just £26 a month. With the ND card, I also got a Carers Card for the National Trust, so I can take anyone with me for free, no ID required for them. I'm happy to take anything I can that will help me stay fit.
I've probably been on / off depressed since the diagnosis but can honestly say I think I'm now in a better place.
My local talking therapies does a group course called Living with a Chronic Health Condition - there may be something similar in your area.
I also had therapy to help me with the really hard stuff, the parts of my condition that I really struggle to live with. You should be able to keep referring yourself for CBT.