You are not really limited at all, the advancement in tech for boards has gotten so amazing that even as a bigger guy you can ride smaller boards with no problem.
I wouldn't say there's no limit at all, but agree the tech makes the range a little bigger. If you're too far outside the recommended weight range for a board, you'll be pushing the envelope on how the board is intended to flex. If the board has OEM specs that include a weight range, try to stay in that somewhere.
and if you order $100 more from there outlet section, such as last years flow "the five" bindings, use the coupon code "whiteout" and they'll take $100 off your order, grabbing you a sweet setup for under $300
that code is only active for another 12 hours i believe, so you should hurry up, and you're welcome.
I have to agree, you're not really as limited as you might think. There are numerous wide and mid-wide boards available on the market from just about every manufacturer. K2, Ride, Lib, NS, Flow, Burton, Signal, Yes, Rome, and others all have wide/mid-wides through-out their lineup.
you can definitely fit on a mid wide board. 26 cm ish waist width. i weigh 230 and ride a never summer legacy 163. size 12 boots fit on it easily. lower 160s would be a good length for you. just look around for an all mountain board. manufacturers websites usually give pretty good descriptions of intended terrain for their boards.