i lay on my tummy til v close to the end... when i couldnt!!! i think it is more for your comfort than anything else. your physio should be able to pad around you with pillows etc which will help. some also have beds for preg women with holes in them.
i wouldnt worry too much that you havent felt her for a while - i never had consistent movements until a bit later... one here and there and then nothing for a few weeks.
good luck!