My favorite whistle, ever (so far) is my Goldie Overton Low F. Excellent, even tone through both octaves, complex overtones, responsive and agile. I find F to be a very nice key on whistle, satisfying and comfortable, somehow (and easy access to Bb, too). And you can play along with lots of Lunasa tunes, if you’re so inclined. It takes some getting used to, playing an Overton, but once you learn what they need, they’re very rewarding. All the usual Overton characteristics apply: good supportive breath pressure required, wrm the whistle up first, etc.
The other whistles I have in the mid-range are a Burke Low G Al-Pro and a Water Weasel Low A.
Burke: I’ve had several Burkes, and kept only this and a high D (which my wife likes more than I do, but is quite nice). Low G: pure-ish tone, very pretty upper register. Bell note could be louder, but is solid. Easy to play, good octave transition, I find the breath demands quite reasonable. Less “character” than the Overton, but a nice change of pace when I’m looking for a pure-but-not-high-pitched sound. Excellent quality instrument. Less volume than the Overton.
Water Weasel: very nice Low A. Somewhere between pure and chiffy; enough chiff and air-noise to give a distinct whistle sound, with some complexity. Responsive, excellent voicing, cool plumbing code right down the front. I had offered this one for sale on the board a while back because I haven’t been playing it, but it’s been sitting beside the computer lately as I waited for a buyer, so I’ve been playing it and I think I might change my mind; a very nice Low A (I like it better than the Burke Low A I had and sold, and it was considerably less expensive).
The other low whistles I might consider getting in future are Grinter or O’Briain, both of which have a distinctive, nice sound. I think PhilO has or has had both of these, so you might check out his previous posts, or send him a PM. I’m spending more time on flute these days, though, so I’ll probably save for a keyed flute first. (That’s your other option, trying flute. Good wooden ones are pricey, but a polymer or bamboo flute will be louder than a low whistle, usually. Great fun, once you train your embouchure.)
I don’t know if any low whistle is going to give you “loud”, but these will all be louder than your Dixon. My McGee Ruddall flute blows away even the Overton for volume, though; low whistles aren’t going to cut through a session without amplification, unless it’s a pretty quiet, small session, I think.
Have fun looking,
Aaron