Went to mompox the other day and it was reeeeally nice. I know this is Cartagena accommodation, but they're close so I thought this was the place to recommend Casa Amarilla in Mompox. Lovely place, nice and chilled out and great service. If you're backpacking you can get a bed for 16,000 which is great value as the dorm rooms are only four bed and you get your own bathroom.