I'm female, 5'9", 140 pounds. Small butt, long legs. I use a 17.5" A/P and jumping saddle. No idea what dressage size I use.
My Dad was 6'4" with small butt and short legs, and used an 18" A/P saddle.
My husband is 6' with same inseam as me, and I can't find a saddle for him at all. He gets his equipment smashed in my 17.5" saddle.
Don't look at a 15" saddle. That's a kid's size. MY 8-year-old just grew out of her 15" and is now in a 16" saddle (roomy for now, but they grow so fast).
I'm most familiar with fitting women. Typically (and very general, here), a petite woman will use a 16"-16.5", an average woman a 16.5"-17", and a taller woman a 17.5-18", depending on butt-size as well, of course. Kids and young teens will use a 16".
You may have difficulty finding a jumping saddle (I assume that by close contact you mean jumping?) that feels right on your tiny butt and still fits your legs correctly. You should probably have a 16.5" seat with longer flaps - difficult to find. You may have to end up compromising a little bit on either flap-fit or seat-fit. If money is of no concern, you can find something to fit just about any body shape. If you're on a budget, a compromise might be necessary.
If you google "English saddle seat size calculator" you should find some good sites. These 2 might help you get started. Any tables or calculators will be estimates. There's no substitute for sitting in the saddle.
http://secondhandsaddleshq.com/saddl...-size-for-you/ http://www.tackwholesale.com/article...tsizechart.htm 
