If you want to fly sparge (slowly sprinkle strike water over the top of the grain bed while slowly draining wort to the boil kettle at the same rate), you'll need either two pumps or a height difference. Height difference isn't too hard to come by though - can transfer the heated water to a cooler and place that on a stand, or can drain the wort to a smaller container below the MLT and carefully pour into the boil kettle when full.
If you batch sparge (add strike water to mash, stir like mad, then drain wort), then you don't need either. Connect pump inlet to HLT to transfer strike water to MLT, get your forearm workout, connect pump inlet to MLT to transfer wort to boil kettle. That's how I've got it set up for single pump, single tier.