Do whatever it takes to get the best performance. I've had singers singing into a hand-held SM-58 in the control room with monitors blaring. This is what it took to get the best performance. This is what it took for the singer to get inspired. Sure there was some leakage into the mic from the studio monitors, but it was not a big deal compared to the awesome performance that was captured. Two takes and it was done.
Holding a mic may not work for everyone, but it's worth a try. With a little good technique, handling noise would be kept well below audible if your mix allows it.
Obviously, you won't want to be holding a condensor mic. Use a stand for it if this is what will best do the job. If you really need to hold a mic, then do so without plugging one in.
Pop filters are great to have and will protect your mic capsule from the "elements" (singer's saliva, boogers, plosives, etc...).
Make your environment comfortable... dim lighting, candles, whatever.