We have lots of bumblebees on our property in Norway. We just leave some parts of the garden completely untouched, with a rich variety of wild plants growing, and they’ll move in there and seemingly thrive well.
Also doesn't require much maintenance so far (which was one of the goals for that patch :) ). Before sowing it last spring I had it covered up for the winter with this tarp that still allows water through, after carefully removing all the weeds and plowing it in the fall. This year, as spring was slowing setting on, I removed the bigger pieces of dead material and sowed some extra seeds on bald spots. Still waiting if that is taking hold.
I'm pretty happy with how it turned out so far, as are the (humble)bees, butterflies, ...