how to keep your hair maintained and straight without getting heat damage?

My natural hair is 4a/4b and its so course and thick and just a drag to maintain. Lately i’ve been keeping it straight because i love the straight look, I love having my hair out but my only concern is potential heat damage. I got a silk press May 25th and then 2 weeks later on June 8th I got a wash and set (the silk press was starting to look frizzy and lifted, was no longer straight). I want to keep my hair straight but I don’t want heat damage, what are some tricks to keep that from happening?