In reply to Queen of the Traverse:
A flex bar is a more flexible bar for crampons. I know Petzl have an explicit one, not sure about Grivel or how compatible different bars are between brands. E.g. https://www.needlesports.com/Catalogue/Climbing/Winter-Alpine-Expedition/Cr...
The idea is that a standard bar assumes you have a certain level of stiffness from your boot, e.g. a B3 or a stiff B2. Stuff like the Ribelle (and e.g. Sportiva Aequilibrium) are B2 in the sense that they have a rear crampon bail but maybe not so much in the sense that they are bendier. Nicer for walking, worse for front pointing.
My understanding is that more flexible boots put more pressure on the linking bar, and so if it's not made to bend then you can fatigue/damage the standard steel linking bars over time. Whereas the flex bars are made to tolerate that.
You could try the Sportiva Aequilibrium boots perhaps, they are a bit wider in the toe than the Trango although the heel can be a bit funny with crampon fittings it seems.
Also, the Sportiva Karakorum HC could be interesting - it's not very light but crucially it looks like it's predominantly an alpine walking boot that goes up to C2 crampons, so I think that will mean they are more flexible than B3s and might be built for a bit more walking comfort. Looks like they sell them as a unisex model so unsure how the toe/heel fit might be. I have a similar pair of boots (Nepal Trek Evo) and they work well for a lot of walking but also alpine capable.
Hanwag, Aku, Lowa could all be worth looking at but I don't know how readily available they really are in the UK.
Alternatively, if you haven't already - perhaps try some B3s which are sometimes a bit roomier... e.g. I fit into Sportiva Nepal Cubes okay whereas Trango Towers are noticeably tighter across the toes. There are down sides to B3s when it comes to walking and stuff but upsides once actually on snowy steeper ground. And I don't find B3s too bad anyway even for a lot of walking, although opinions differ.
Personally for boots I'd compromise basically everything else (except maybe warmth but less of an issue in summer alpine) in order to get a good fit.
Edit: one option (if you haven't already) is to basically call or e-mail all the decent UK shops with a list of the boots you've already tried and see if they have anything that's wider in the toes, or can suggest something. Rock+Run, Needlesports, Joe Brown/Climbers Shop, Outside...
Post edited at 18:16