Cressida Maris is a nice combo, but you're right, it's a bit too close to
Jessica.
With
Mariska, I'm biased - for one it's a Hungarian name, and of course I should like that it's gainging popularity in the US. On the other hand, it is considered a hillbilly name in my country, especially in the form Riska, which is the No 1 cow name. Also, Mária (of which
Mariska is the pet form*) is really frequent among eldery (55+) women.
Theodosia is really nice, I like it (and also
Theodora). A great name IMHO!
* this sentence might not be grammaticaly correct, but I'm just too sleepy right now to think it over