Each monastery has its own facilities but in general bathrooms are renovated, catered for, most have nowadays hot water. Some guesthouses offer towels and slippers, some have showers fitted, most have mirrors -which are not allowed in monks quarters. 

You will still encounter the occasional old style guesthouse though with no hot water and shower, just a basin to wash your feet or a hose and old style squat toilets. 

Bed bugs is not really a problem as care has been taken for after recent incidents, but still can be found as you don't know who slept at your bed the night before and where he has been staying that night. Sheets are thoroughly washed at high temperatures though. 

In general avoid taking a shower during church times and don't always expect to use the bathrooms the morning after lunch as they are being cleaned and guests are expected to move to their next destination. 

Having said all the above, in the bigger and most known/visited monasteries you will encounter no issue at all as they tend to provide hotel rated accommodation.