Guidance for combination hair!

New here - hi!

OK. My hair seems to be changing somewhat -- I am 36. The top of my head seems to be 3A. It has highlights on it, which dries it out a bit and roughs up the texture somewhat too. Underneath, my hair has always been straighter and finer but it's getting WORSE as I get older. It doesn't have color on it and seems to be a 2B wavy type hair.

It is driving me CRAZY. I feel like the under-part of my hair belongs on another person!

How can I reconcile my two hair types?! Cuts, products...? Right now my hair is just past shoulder length. I don't have bangs -- those hairs are past my jaw when they are not naturally curled.; when they are, those front pieces hit about chin length. They can get spirally but of course the underneath pieces do NOT curl much at all.