Alaska's policy on second seats seems quite fair. Those needing the extra room can purchase two seats (both at the same fare) and receive a refund if all flight segments operate with empty seats.

The policy can be viewed at: http://www.alaskaair.com/as/www2/hel...econd-seat.asp

Note that the possibility of refunds does not apply to those needing the second seat for their "cello" or other valuable cabin baggage.

And "normal" sized persons can't expect a refund for a second seat. You qualify if you can sit comfortably with both armrests down. In practical terms, you probably qualify if you need the seatbelt extention.