Haven't ever used a bivy so can't give you any advice there.

I would suggest that whatever you get, try it out first. If it's a tent or a bivy go to a store that sells it and have them set it up and get in it. Spend a little time in there and you'll get a decent idea of how it will work for you. Not as good an idea as you would by spending a night in it but unless you can rent it, that's not an option. Try out different models so you have something to compare it to.

I would say the same about a sleeping bag-get in it, see how it feels, and a backpack-put it on with some weight in it and walk around the shop. Again, if you try a few you'll a better chance of finding the right one that's for you!

As mentioned, Vancouver Island is a very wet place. You could be spending a lot of time in whatever you end up with. There are one person tents out there that don't weigh much more than that bivy.

Good luck!