Any suggestions on how a small office (~15 people) can have a napping area without taking on any additional custodial work?
An ordinary couch that's long enough for a person to lie down on will do. If it's vinyl / plastic covered, cleanup is a matter of wiping it down periodically. Add a couple of small cushions to act as pillows (periodically replaced for hygiene) and, voilà, you're done. If the soundproofing of the nap area is less than optimal, add an inexpensive white noise generator to help mask ambient noise.
Employees can supply their own blankets, etc. (I can't imagine that people would be particularly enthused about the idea of a shared blanket anyway.) I use a cotton hoodie in place of a blanket since the hood can be pulled down over the eyes to block out light.
Also, on behalf of myself and others, thank you for being a considerate employer and providing a nap area. I, myself, suffer from treatment resistant insomnia and I know many colleagues who have had less than a full night's sleep because of their newborns or children who would have desperately welcomed a place to nap.
But really you just need a closet or a small room with shutters. My building/shop had about 100 people and with those two recliners and a small futon, it worked out pretty well. There were never more than two people down there and there was an unspoken rules about .. well .. not speaking. Some people would go down there to meditate. You'd hear the chimes on their phone app.