You can a single hotel room together in almost all hotels in Iran. It is a common practice and the hotels do not even ask if you are married. Of course, there have been some rare cases where a few hotels have refused to give a single room to male and female companions. This usually happens in smaller guesthouses or those run by a governmental department. You’d better check if you are not sure. Generally, you can easily get a single room and enjoy your privacy. Some hotels have a free atmosphere where females can take off the cover. But it is nothing legal.