I use a Dirty Bird scuttle and love it. I fill it with water from a hot shot and top it off with tap, put the brush and some more tap water in the top bowl, and let the whole setup set during my shower. By the time my shower's done the inner chamber has cooled to the perfect temp (too hot and you can't build any lather) and the brush has warmed up.

I use Julie's 1.5x size. I couldn't speak highly enough about the work she does and the service she brings. I've also seen people do head-to-head tests of heat retention and the DB scuttles stay warm longer than the competition.

If the price tag seems steep there's a potter on eBay who sells scuttles more in the $20-$30 range I've heard good things about if you want something to make your lather warm but aren't so interested in shelling out for higher end performance. It could be a good best of both worlds options.

(and PS hi to everyone, first post on this forum, established DE shaver getting increasingly interested in straights here)