There’s not a whole bunch one can do about frizz on the top of the head. Maintaining your locks will help reduce frizz, but it won’t completely eliminate it. Here is a post by JR about that.
However, if you have a special event, you and drastically clean up your hair by twisting with aloe, pinning the twisted roots back, and letting it dry that way. The aloe will help set the hair in place. If you sleep with your head covered at night, this tidiness should last for about a week (or until your first wash), so it might be something you like.
As for your hair thinning, if you tike multivitamins and watch your diet, there’s not much else that could be done. We are not professionals though, so if it is a concern of yours, a licensed dermatologist should be able to offer the best suggestions for you.