Those are good suggestions. We've tried swapping kids with our friends, but they're really overwhelmed with parenting in general, and my kids' patterns aren't at all compatible with their lives (my kids rise early, eat often, and are really active - our friends rise late, don't expect to have to do breakfast when the sun comes up then food every 2-3 hours, and generally have a pretty quiet household). They've watched the kids before, but it's clearly been a stressful experience for them. I don't really have any other good friends where we live; I don't make friends easily, and I don't keep many good friends in general. I only have the energy for one or two close relationships outside of my marriage/home life.
I think for the time being, I need to rely on the beautiful weather and the fact that my kids know me. If I ask them to play outside and tell them I'm worn down, they will generally give me space and entertain themselves pretty well; we also have a great neighborhood with lots of kids to play with outside. I have to let go of the guilt for sending the kids to be away from me when their dad is gone, too. I hate that part of this.
At least with my husband gone, I can get plenty of quiet time to restore after the kids go to bed without feeling like I need to continue to interact. That on its own can be stressful when I start feeling like this.