How do you do cardiovascular exercise in an upstairs apartment?

Im trying to lose twenty pounds in a month an a half.

This isnt impossible since i have a fast metabolism and the only reason I am 148 is because I had a child recently. I also burn calories breastfeeding.

Im trying to be respectful to my neighbors

I need a sufficient way to do this without jumping or running in place.

I cannot diet while breastfeeding. It depletes the supply.