For Musa spp. propagation (not specifically M. nana) I have used P5 agar and CA (charcoal agar). I don't know if you have tried this or you referred something more simple.
There are a lot published literature for banana in vitro propagation.you can use the simple MS medium with BAP as cytokinin in a concentration of 1 to 5 mg/L and auxin at at 1 mg/l.