I have a few, I would say the most key thing is a pair of very close fitting knickers with a perfectly placed pocket to keep the vibe in the perfect clit spot contact at all times. Without this, even the best vibes can be disappointing.
Lovehoney used to sell this bra set, which thankfully I purchased in great numbers. The bra is great for practical everyday use, but the high leg thong is perfect for vibe placement and security with a built in snug pocket. Your wife needs something like the thong from this set to get the most from whichever vibe you settle on.