I wear my hair straight in the Summer alot\ without any problems. I think using very moistuirzing products and a good serum helps alot, I rollerset my hair after each wash and at night part it in front and then take each side like I was making pony tails and carry it over to the opposite side, pin it in place and then tie my head with a silk scarf. Wrapping my hair that way doesn't put any stress on my hair and causes no breakage, but keeps it straight. Also I use the twisty rollers at night if I want nice fluffy curls.
So far my twist-outs come out in between wavy and crimpy looking, I think I need a little more practice.