Yeah I've been there before, but only in June, I'd imagine its a little cooler in January!
I've stayed at the hotel Jacques Villeneuve & Coulthard co-owns, called the Columbus. Its rather nice!
http://www.mrandmrssmith.com/luxury-hotels/monaco-hotels/monte-carlo-hotels/columbus-monaco/
When we stopped at St Tropez, we didn't stay in the town, we stayed the other side of the bay in St Maxime at the Amarante Golf Plaza - lovely place, highly recommend and great value. Stunning views from the rooms.
http://www.laterooms.com/en/hotel-reservations/83823_amarante-golf-plaza-4-sainte-maxime-face-a-saint-tropez.aspx
Best Regards,
Gaz.