A good next key for a whistle?

[KNQuail]

I don't play with anyone - just noodle around with the whistle for my own enjoyment and amusement - so I really don't need more than one whistle...but of course I've picked up a number of whistles anyways, just because they're cheap and it's fun to try them all! Probably my favorite one is my Dixon Eb...such a great sound! I also love the Gen Bb...so I'll say get one of those! (Or both!) I will agree with others that expanding one's whistle collection is a slippery slope. The addiction keeps getting stronger...I recently acquired my first low whistle, a Pipe Makers Union carbon fiber whistle in F. No need for a low whistle, but I saw it at an Irish festival, played around with it for a few minutes, and couldn't put it down.

[walrii]

The version of "Off to California" I know is in G. Having said that, the tune also has no Cs, sharp or natural, so I suppose someone will chime in with an discussion of gapped modes or some such. Which would be nice, actually. I didn't quite follow all the theory the last time.

Edited to add: I'll leave the answer to "Which whistle will I need?" to the experts. In answer to "Which whistle would be nice?" I vote for a Jerry Freeman-tweaked Gen Bb or a stock Gen Bb, depending on your budget. Either is a nice whistle that plays low enough to easy on the ears, yet is small enough and light enough that you won't be making the jump in technique required for a low whistle.