That comes down a bit to technique and the outline of the board.
Chord means length of the fin at the base. C drive fins have a long chord. For example:
www.surfnvs.com/products/c-drive-thrusters-apexOr, you could take your board to a board repairer and get a longboard fin box fitted. Probably cost about $120. Easy to do. Then you can use a longboard fin (up to 11" long) or use a 7-8" fin with some small side fins...
If you want a easy to paddle straight board... a longboard style SUP with a big centre fin will go the straightest...