For reference, here are the measurements of the rui last in size UK7 and UK7.5 given to me by Luisa.
> L 294mm shoe sole 7UK - L 298mm shoe sole 7,5UK.
> W 105mm shoe sole 7UK - W 106mm shoe sole 7,5UK.
> L 276mm last(insole)7UK - L 280mm last(insole)7,5UK.
> W 098mm last(insole)7UK - W 099mm last(insole)7,5UK.
> Foot 25,6 cm 7UK - Foot 26 cm 7,5UK.
My feet are 26cm x 9,6cm or thereabouts. I just placed an order on the country boot in UK7.5, which is what Luisa recommended. I did specify that I want to be able to wear somewhat thick wool socks in them, though. If it was for a regular shoe I probably would've gone with UK7, but my feet aren't that wide anyway. Just hope the sizing works out!