Thought I’d update this.
I found an interestingly named Cubot King Kong Mini phone. It is ruggedised and apperently waterproof, although not officially. Only £90 new, but I found a very lightly used one for £55 so took a punt.
Seems very good so far. The screen is easily readable in bright sunlight. The touchscreen works well with one of my pairs of gloves, but not the other, might add some of that conductive thread. I was a bit worried about battery life but in flight mode, just using preloaded maps and GPS, it dropped about 12% in two hours. I may use it with a sim for more map options but so far with viewranger and trailforks it has been good. Obviously being Android there are lots of options.
I’ve made a quick bracket. Its easy to use and read here but it seems a bit exposed so I might make one that tucks it out the way a bit.
Hard to get the scale but it is pretty compact. Might actually be a good phone if you want something small