I'm no fan of wireless at all, but I've recently bought a cheapish wireless headset mic (Thomann T-Bone Free Solo) specifically for when I'm singing BVs while playing double bass.
It's such a physical instrument that getting pulled out of shape by the need to get your mouth up close to a normal mic is a real pain, quite literally sometimes.
I like to use good kit, and the wireless Lavalier mic is nowhere near the quality of the Beta SM57 I use with a mic stand, but it's horses for courses, innit?