You never said anything much about what kind of boat you will be on. That makes it rather hard to give good advice. I thought you meant you would be on a small private boat (power or sail), but it is beginning to sound like you will be on one of the regular larger tour boats?

If so, you probably don't need to bring your own PFD at all. The tour boats are all well equipped with proper PFDs. Before you depart the dock, the crew usually give a quick briefing about where the vests are stashed, how to put them on, etc. If they don't brief you, ask. The larger tour boats are also well equipped with rafts. In the unlikely event of trouble, you would probably be better off not using an inflatable PFD which would require shedding your jacket. Keep you jacket on, you will want it even if you go in the drink. Just put one of the boat's big PFDs on over your jacket. You will be much warmer if you end up in a raft.

Another reason not to bring your own inflatable if you fly commercial up to Alaska is that the CO2 cartriges can cause problems with airline security. Apparently TSA doesn't object, but leaves it up to each individual airline. Some airlines allow them, some don't. See http://www.inflatablepfd.com/faqs.html. Sailors have had lots of trouble with this, for example see Cruisers Forum. If you do want to bring them, definately check with your airline in advance. Otherwise you may need to aquire re-arm kits when you get to Anchorage.

If you really really want to bring your own PFD for riding on a tour boat, and want to be relatively inconspicuous, you might want to consider a "float coat". Check out the Catalyst Flotation Jacket or the Integrity Vest. They look nice, like ordinary clothes, they are warm, and are USCG approved Type III PFDs. The coats, in particular are also good because they provide some insulation in the water, and can increase your survival time. Standard disclaimers, I have no connection with Mustang other than having used and liked their products.