That "prone to frizz" mention tells me that, like me, your hair was never really straight. You just thought it was, because everyone told you it was, and you treated it like straight hair. But generally speaking, frizzy hair is not straight--at the least, it's wavy. I'm almost 55, and up until a few years ago, when I first typed my hair according to longhair principles, I thought my hair was wavy (and frizzy). Then I began to realize more and more that it was actually curly, and today, after several weeks of CG, I have a full head of curls that I thought I could only get with a perm, lol (OK, the rain lately helps, but you get my point). I can actually pull a lot of curl out over time with combing and some oil, so if I was still treating it as wavy/straightish I'd probably think that was its natural property, but it would only be disguised.
I also thought that my hair somehow "got curly" as I aged, but thinking back, that's really not true. My attitude towards it and the way I care for it has changed, but the overall hair has remained the same except for some graying.
It took me a while to find something that worked for CO, so you may have to experiment a bit. A lot of people like Suave or VO5 conditioners, but they don't work for me. I suspect that some of my difficulty may have to do with my water (hard well, minerals), but I don't know. I did find products that CO well for me, and now I'm very happy with my wash routine. Good luck and enjoy learning!
Former longhair, now CG, living in N. California where the fog meets the wind
3a/b, fine, normal porosity/elasticity, high density
Conditioner wash and style, sometimes with a dab of BRHG.