Certain things may limit what exercises you can actually do
Your age~yeah I know some older people can still do stuff lol so that ones a bit controversial but nonetheless at say 60 you are going to be able to do less than when you were 20 not everyone ages as well as some
Do you actually have any underlying medical conditions?
Advising something too hard core with out knowing that would be bad to be honest
What ever you decide to do don't go crazy immediately or you will be in agony for days if your back muscles aren't used to it
If you have a garden you could set aside a small area that you just use for digging over. Digging certainly does help with back strength and legs too