Kaushal
For a female chastity belt I would recommend a Neosteel, with an ergonomically shaped, high waist band with a single cable rear. I'd choose a secondary shield with it's own lock or, ideally, a secondary shield that is permanently attached. I'd make sure to order lock posts that can take security seal. I'd also order a high security lock.
The secondary shield will help prevent pinching on the hard floor, and the ergo shape will permit greater movement. The wearer, your fiancee will however have to make adjustments to how they move and sit. After a time the belt should become part of them and be less of a problem.
If they are skinny I'd definitely choose a waist rather than hip model for security's sake. (There's just no point in putting up with the inconvenience and doubt of a belt that isn't secure). Many waist band wearers on the forum report that movement is okay.
You mentioned in "introductions" that you (wisely) plan to allocate time to get used to the belt, make sure that in the early days you bend and subtly reshape the belt each time you try it. The fit should be perfect (in all positions) to avoid discomfort, pressure points and abrasion in use. If the belt is due to be used immediately following marriage, be aware that radical readjustment may require return to the manufacturer and this can take quite some time.
Best wishes to both of you.
