I would think a pot about an inch or two wider, and not very deep, would be ideal at this point. I would advise against disturbing the roots at this time of year (assuming you're in the northern hemisphere) but a simple repot (lift, drop and fill) should not be problematic. Make sure the new pot has holes at the bottom. Use fast draining soil (like regular potting soil mixed with an equal volume of perlite, pumice or gritty equivalent) and wait a week to water afterwards. Be careful not to overwater over the winter (wait for the soil to dry out at depth before watering). You may not see the plant make any big turnaround until early spring.
