Short Term Apartment Rental in UB

I'm looking for a studio or 1 bedroom apartment in or near district 13. My budget is 350,000 - 850,000 per month. I need the apartment as soon as possible and I can move in right away. It would be great if anyone could give me a tip for a short term lease (1 - 3 months), because I don't know how long will I stay in Mongolia.

I need my own place because I might have a 2 year-old visitor and his mother at night. So guesthouse is not a good option for me.