I can't speak to whether this relates to what you're experiencing or not, but this is my own experience with wobbly legs.

I'm coming up to my one year anniversary next month (Feb 19). I've found a direct relation to how strong my body feels, but especially my legs to how well rested my brain is. When my brain is well rested, my body feels stronger.

For me, this is particularly important because after my injury, I developed some gait issues that have made getting around more difficult. I've been working with a physio to correct the gait issues, but progress has been slow.

For my brain to be well rested, its meant actual sleep, not just quiet rest and quiet activities, though they are important as well. I've not been entirely sedate though, not as much as my doctor and physio would like, as I'm still hobby farming, livestock need to be fed, watered and cared for no matter how crappy you feel and I refuse to sell them on, as all my care providers insist is necessary.

So I'm still doing chores 4 times a day, hauling water buckets 6 times a day because its been unreasonably cold here, I move all the hay and feed myself, though I do have a front end loader tractor to deal with the manure end of things, which makes the work possible, though I still have to hand fork it into the loader, but then I don't have to haul it 400 ft to the pile, thank goodness!

In between chores, I do rest and I ensure I get a 3-4 hour block of time once during the day to sleep, plus 8 hours at time. I don't suffer from some of the insomnia issues that other people seem to, in fact, I suffered from insomnia most of my 40 years before my injury and now its the opposite, I've finally learned to sleep.

To help with the weak legs when I'm out in public or if I'm walking around the property here with my hands empty (rare!) I do use a cane (with a rubber tip or ice grip for safety!) The cane has been very helpful for adding confidence in places where people move very quickly... also keeps children from running into you in public places.

I'm not sure if any of this will help you, but maybe see if your legs feel any stronger right when you wake up or see if you feel stronger and more confident in general if you move around with the assistance of a cane.

Also, I know you mention stretching causes you to feel poorly the next day, what about extremely gentle stretching, barely coming to the end of the range of motion and just holding it. Maybe you are expecting too much of yourself?

Best of luck.
Starr