Gesthus Selfoss is actually a fairly large (& popular !) campsite for tents, RV's and of course cabins (which we rented). The cabin was comfortable, clean and for us (we had a rental car) very conveniently located. If we wanted to, we could have prepared meals (has 2-burner range, fridge, etc.)
By the way, Selfoss is a very nice town and not far (15km) from the Kerið Crater Lake. Do book early because Selfoss is a popular stop for Golden Circle travelers. Two excellent restaurant experiences for us were: 'BK Bakari' in the morning (coffee, made on site breads, pastries, sandwiches) and 'Tryggvaskali' for dinner (amazing food & service; put a reservation in place)