If you can take a half decent picture then get yourself to a model agency.
I think is in sunderland
Is huge and has models from Sunderland.
A lot of models want underwear pictures as it shows off their body.
You'll get a better quality girl if you shoot in a studio.
Most girls will do it for free if they are going to get something out of it.
So you will probably be better off spending the money on a studio and lights than the girl!
Its always good to do a head shot of the girl as well.