The Burton Fish is legendary for pow riding. At your weight, I would definitely go bigger than 160 especially since it will be a pow-specific board.
The reason you had a bad time on a 161 before is probably due to the board itself rather than the length. Maybe it was a super torsionally stiff board? Hard to edge-to-edge on?
If you want something for more playful pow days, get something mid to mid-stiff in flex. The Custom Flying V is a good board, but it's a love/hate thing. You really do have to try the Flying V shape to see if you like it on the Custom (they make the "V" in the Custom more pronounced than their other boards for some strange reason).
Check out the K2 Turbo Dream for your more playful days. I can't recommend this board enough for people who ride powder, but want something that's going to be playful. I used to own one and took it out to Tahoe for 3 days of shredding 2feet + of fresh. I had a TON of fun on this board. It floats well and is damp enough without feeling absolutely dead underfoot. Turning is quick thanks to the softer torsional flex and a deeper sidecut.
This is just a link for you to see it. Sbnet doesn't deliver overseas without significant third party costs.
K2 Turbo Dream Wide Snowboard 2012
Also, if you can get your hands on NeverSummer, they have more than a few ideal boards for you. For powder days, a Raptor comes to mind. I think the Heritage will be an excellent choice for your main board. It's plenty damp, but still has some liveliness underfoot. NeverSummer's R.C. shape is excellent. You get the rocker playfulness between the feet for freestyle fun and float. Their camber section starts just outside the bindings so you don't feel it until you engage an edge. You do have to get used to this shape though especially if you've never been on a hybrid rocker of this type.
Ride is another brand you should look into. The Highlife UL comes to mind, but that is a stiff board. Very fun to carve on though and it's beastly on good snow. Edge to edge on the Highlife is superb.
Oh, you'll probably need a wide snowboard.