Mt. Fuji in December is not a good time to climb, especially for novices. Conditions are poor and there is little to no support if things go wrong. There are several incidents each year of inexperienced climbers being stuck (or dying) due to sudden bad weather.

However, if you want to spend a day relaxing in a hot spring you could make a booking at an onsen hotel at one of the five lakes at the base of the mountain. (I would be careful when choosing a hotel/ryokan due to your tattoos, however.)