You have a lot of detail on your dress so I would go for a single layer simple veil if you decide that you want one. You don't want to block out the detail. I'd go for a full-length chapel length veil, rather than a shorter one, as I think they flow better with fishtails.
Honestly I don't think dresses like yours need a veil as such as it's beautifully detailed at the back already, although I've ended up with a veil despite picking a dress that really doesn't need a veil at all, so do ignore me
I'd either go for a short elbow length or a super sheer 1 tier cathedral length.