I presume the flat is rented by the people upstairs and the landlord lives elsewhere. You could explain the problem to the landlord and ask if he would consider insulating the floor with fibre board, and tongue and groove chipboard on top, and finally with carpet and underlay. Other than that you would have to insulate your ceilings. A friend had similar noise problems when the flat above changed hands, the new people were heavy footed and on polished hard wood flooring. The previous occupiers walked bare foot so no problems. When the noise became so unbearable she insulated the ceiling it cost around 2K in 2002 for a 12x9 foot room and she felt that it only stopped 20% of the noise. It did not stop the impact or vibration of anyone with a heavy tread. What was more effective was when the next tenant had fitted carpets layed. She also invested in ear plugs ?2 per set from super drug.