Heat is my friend. I used heat weekly when I was relaxed and my hair was always long. I think harsh/frequent brushing and wrapping my hair every night was waaay more damaging. The key for me was to air dry and straighten with a big barrel curling iron (using a flat iron was asking for trouble).
Now that I'm natural the use of heat is keeping the split ends and single strand knots away. I avoided heat for well over a year and my hair grew at a good rate, but my ends looked crazy (and I deep conditioned/wore protective styles, moisturized etc.). I was able to wear my hair curly with no problems but the first time I straightened it...... my hair was looking a hot mess.
I got ~3 inch 'trimmed' Sept. 2nd and she cut my past shoulder length hair into a bob. It would barely fit into a bun
erplexed. I began flat ironing once a week, but still wearing my daily bun and my hair is already back to where it was before she cut it. I attribute these great results to OCT/Gro-aut and - wait for it - HEAT!
Keep in mind that I always use a heat protectant. I loved Aveda USC with a little Redken heat glide when I was relaxed, but I've moved on to Sabino moisture block.