You are unlikely to get what you want without the bathrobe option as that is the way it is done in most clubs. By far your best option is Sharks in Darmstadt. Fly to Frankfurt, take a bus directly to Darmstadt from the airport and then either a taxi or Bus R from the bus station. Lots of reasonably priced hotels in the area.
On a weekend you can count on up to 100 naked available girls. Only trouble with Sharks is that, after about 11pm, the other punters can be not such pleasant company, so your best bet is to be there in the afternoon to get the day shift and then early evening to also take advantage of the night shift; most girls are arriving around 7pm.
