i would like to recommend Come On Guesthouse.
Comfortable, good service and everything is good.
it is quite near to Chungmuro Station Exit 1, and it is in front of convenient mart GS 25.
just need to walk about 100m from Exit 1 to reach the guesthouse and you will pass by 7E too.
and the price wise, it is very affordable for backpackers like us.

and don't forget to go to SulBing or any bingsoo shops there!