A straight comb is more often called a single comb.
Also there's one other small nearly flat comb type and that is the cushion comb.
Also there's one other small nearly flat comb type and that is the cushion comb.
From the (parent) chickens you have listed, it sounds like you have the options: v-comb, straight comb, v-straight comb, pea comb. Of those four, your picture looks most like a pea comb, but just to be sure, can you give us a nice, high-definition picture of just the comb? Sometimes, it can be hard to tell, with chicks.
Incidentally, there are three other types of "flat" chicken combs I've seen. Rose combs are flat, but tend to extend back a bit and are just a bit lumpy. Pea combs have three rows (like three, separate, entire straight combs right next to each other, but very short and small) and are mostly flat. Strawberry combs are just flat. Walnut combs (silkie combs) are like strawberry combs, but wrinkly.