Can you raise the shower tray ? or is it a flush with floor job. Have u looked at another route. If do have to pump the waste make sure the pump is on a rubber mat on a paving slab otherwise your neighbour below will be disturbed by the noise and vibration.
Saniflow have a range of suitable pumps and I would be tempted to fit a slighly over specification model. centralheatking
Sanishower will pump it 50m