A skinny type of belt does not restrict your mobility but still offers enough support to make a significant difference. Leather belts with smaller width in the abdominal area than in the back and less than 7mm in thickness are perfect for front squats. In terms of width, the best choices are 3-inch and 4-inch. Another solid option is a nylon belt, which is more comfortable, but most of the time a leather one is superior in terms of support.
The idea of using skinny belts for front squats is implemented by most Olympic weightlifters in their training, although the IWF (International Weightlifting Federation) rulebook allows a maximum width of 12cm compared to IPF (International Powerlifting Federation) where the maximum allowed is 10cm.
A powerlifting-style belt has its benefits for sure, but using one for front squats is not the best idea.
If you feel discomfort when doing front squats with a 4-inch wide leather belt, the best shot is to try a 3-inch one, which limits the belt from digging into the ribs. For problems such as discomfort in the hips area (belt digging into the hips), a nylon belt with a contoured design might solve this problem.