My body is still used to working out. My supporting muscles are strong. I've got fat but I'm not soft. My joints honestly are fine. Surprisingly so really. Hell I can still almost bench press my body weight. My leg and back lingering injuries are large scale muscle tears. I'm just trying to find some non weight based exercises to help me strengthen those without hurting myself again.
But I still can't do cycling. It's my thigh that is damaged not the knee and I don't have access to a pool. I need to find a cardio exercise I can do without destroying my leg in the process.
It's pretty hard then to give you optimal advice without seeing you in person and without seeing what you're actually able to do and what not.
If you're handicapped with your leg, you may try an indoor rower. Normally there your would also use your legs, but you can reduce the leg motion to a level that is comfortable to you.
But again, it's hard to give you advice without seeing you in person. So I'd be really the best to ask the physiotherapist you've talked about.