Hiya op...
I can only give you my experience, so t may not work for everyone.
I suffered a mental breakdown in my early fifties that had me not hardly moving at all for roughly three and a half years.
Ten years ago (turning 60) I gave up any animal based food, I purchased a rebounder (I found it more beneficial than jogging etc) I started very very mild exercise.
To improve my flutes in particular, I read from an advisor in his fifties, that one should be able to achieve at least thirty squats.... I'm quite stubborn, and I thought I'm gonna try... so whilst I brushed my teeth (two birds with one stone if your time is tight) I did ten squats... kept that up for a week and upped it gradually to the magic thirty.
What was gratifying was that my partner didn't know I was doing this.,and after he playfully had given my bum a squeeze, said omg, what have you been doing , your bum feels amazing...
I asked him to look, and he said there is a definite difference, and he said he can see it when I wear my jeans...
Years later, I now every morning do over a hundred.
So squats made a huge improvement for me.
Additionally, I find it easier to get up from the sofa, and when I'm in a shop, and an item is on the bottom shelf, I can now get up without needing to pull myself up via another shelf... it so improves self confidence too.
If you can manage sit ups, they have made my tum muscles improve too... I don't think I do the proper full sit ups... all I do, is sit on the side of the bed, put something on the floor to hold my feet down, then sit up straight, and lower my upper half down, but not all the way to the bed... maybe a tilt of halfway..
I started off with ten, and then gradually increased that number.... warning!! The next day, I couldn't cough without hurting, ouch!!!
That does go away with repetition, I do it every day.
This has resulted in a very firm tummy, and my partner can feel my abs (I can't see them) but he can definitely feel the definition under my skin.
My next aim is to try to contain my bingo wings... gee, I hate that term!
Good luck, you can do it with determination and motivation... I find it easier if I'm cross about something, as I can vent out my anger via exercise.
My now morning routine takes no longer than forty mins... but please start off slow, and build it up...
I hope it works for you, whatever you try.