The Current
Measure your feet and use the exact boot maker's chart, then test the boots inside your actual fins. Width, instep, calf opening, sole and sock thickness can matter as much as the number printed on the label.
Painful dive boots need a fit check, including the fins worn over them. Toe pressure, a high instep, seams, grit or strap tension can all matter. A thin liner may reduce friction but cannot make an undersized boot roomy.
Thin Lycra liners, neoprene socks and protective-soled dive boots serve different purposes. Choose for warmth, contact protection, entry conditions and fin-pocket fit. Adding a sock changes the footwear combination and may make a tight pocket less comfortable.
Large dive boots must match foot length, width and instep volume as well as your fin pocket. Try them with the liners you plan to wear. More length does not necessarily solve forefoot pressure, a high instep or an incompatible fin.