Ditto on the brushed blue. That shirt is excellent. I'm not sure if this will apply to this particular fabric, but I have a few Epaulet flannels (The purple herringbone and Gold buffalo check) and I wash on cold and hang dry them. They look just as great as the day I got them.
I live in SoCal and wear my taupe heavyweight twills all the time. I just don't wear them much during the summer. I would say there's a good 7-8 months out of the year where they see pretty regular wear.
I've had some walts and rivets let out in the thigh and the waist. My tailor didn't have any problem, but one thing to note is that there isn't a whole lot of fabric to let out in the Rivets (I'm talking about the thigh and seat not the waist). You'll definitely want to keep that in mind.
Most likely you will take the same size in both those lasts. For what it's worth, I'm a 9UK in both and both lasts fit my feet pretty similarly with the forest last giving me a little more room in the toe box.