Pillow tops that are separate from the mattress can slide off to the side after several nights. Also, fitting your current sheets over the extra layer could prove to be difficult. Even if the sheets seem to fit, they sometimes quickly pop off.
If the pillow top is attached to the mattress, you cannot flip the mattress over to the other side unless each side has a pillow top. You can still turn it, switching the head and foot around. Both flipping and turning the mattress on occasion help to even out the mattress’ use to prevent or delay sagging and broken springs.
Sometimes a pillow top mattress or pad feels like the perfect fit at the mattress store but, once you sleep on it at home, you realize it's too soft and does not provide the back support you need. Firm mattresses typically provide the best back support, so if you select a pillow top, it should be firm, not soft. A foam pillow top, for example, usually provides more support than a down pillow top.
You might need to buy new sets of sheets with deeper pockets to fit over the top of a mattress with a pillow top. Also, in general, pillow top mattresses are more expensive than similar mattresses without pillow tops. Pillow top pads are also an added expense but can be transferred to your next mattress. If an infant sleeps in bed with you or if you nurse an infant in bed lying on your side, you are adding an additional risk of sudden infant death syndrome because of the soft bedding.