Types of harnesses are going to fall in roughly two categories - the type that have a strap between the legs and the type that fit more like a jock strap. My lady friends seem to prefer the kind that fit through the legs because it fits better and gives them more control of their penetration strokes. Just like with a guy, being able to control the dildo is important for comfort and excitement of the bottom.
If she wants one just to use on you on an irregular basis, you are probably better off investing in the cheaper ones. But if she is going to use it more often (with you or anyone else) then do some shopping. Leather is good, but remember that it absorbs fluids and is very hard to keep clean and disinfected. Look for something non-porous.
The feeldoe is supposed to feel interesting for the lady, giving them a bit of a feel of having a real cock without the straps, but it does have its limitations. Chief among them is that it's just one size. A dildo harness will give you the ability to try many different types and sizes and firmness of dildoes. Plus a number of the harnesses allow for toys to be inserted and retained by your partner, so each time she drives into you she might get clitoral stimulation, or even have a dildo inside of her being thrust further inside. You are only limited by your imagination!!!
Check out Babeland (
www.babeland.com). It's a Seattle store run by ladies and has an excellent reputation, not to mention a very nice and wide selection. Also look at Madame S leathers.