I also have fine, thin hair. Some people will say they have fine hair but alot of it. So, I see it as two different things. I have fine hair but I also don't have much hair - so thin.
I would say if your products and shampoo/condish are working for you, I wouldn't change anything. Don't fix what isn't broke. If you're getting good curl formation and no frizz and you like how it looks then I wouldn't change. As far as growth, I don't have an answer because mine will also only grow so long and then it just stops. When I was a kid, I had waist length hair so I don't get it. Maybe someone else will chime in here. I would also like to grow some length IF it doesn't start looking stringy.

Natural hair color - dark brunette
Fine, thinish hair/3a, 3b