I have naturally curly hair that I straighten as well... I have recently started using the new Dove shampoos and am impressed w/ the silkiness of my hair- whether I straighten it or leave it curly... I also use Keihl's Creme w/ Silk Groom on my ends.
I also will dry my hair curly, use a 1 and 1/2 barrel curling iron to pull most of the curl out of it and THEN run a flat iron over it... Takes a LITTLE more time, but the curling iron does less heat damage than the flat iron... Helps a bit w/ the dryness.

Aveda Custom Control works GREAT on your ends if you want to do a really choppy / textured look, or a teeny bit over frizzies smooths!
Good luck!
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aas