Leaving aside the utility of BMI (meaning varies with population due to environmental (ecological and dietary), cultural, and genetic factors, not useful in pregnancy) which I guess is why you want to measure adult stature. I think you should plan for the worst and make these in-country. You need DIY measuring tapes (2 metre steel tapes should be good enough) or dressmakers tapes (if you can get them long enough ... or ... you could fix a 1 metre tape with the 0 cm mark at, e.g., 1 metre above the ground and correct measurements for this), some epoxy resin (for the steel tape) or contact adhesive (for the dressmakers tapes), lengths of planed lumber of (e.g.) 50mm by 25mm by 2000mm, and some sticky tape. Break open the tapes and glue them to the lumber using the sticky tape to hold them in place until the epoxy dries (steel tapes) - no need for sticky tape if you use dressmakers tapes and contact adhesive. You'd need to fashion a cursor. All the materials and the craftsmen to make these should be available in any town.