I guess seeing a physio isn't exactly an option in these Trying Times
AthleanX's videos on the subject are pretty good. He's a bit of a meme in online fitness communities and can't keep his shirt on for more than 2 seconds but he knows his stuff. He used to be the head PT of the Mets. Here's his instructional playlist, it starts with lower back stuff and there's good videos about posture too:
(you need an account to see links)
Btw congrats on keeping up the workouts in any way you can
I would go mad too if I couldn't move (I'm quite spoiled with a decent home setup). There's tons of bw fitness content out there too! Pushups till death or ascension into saiyanhood