We didn't intend to use a bumper because of the risks of SIDS but ended up buying one when she was a few months old and was alot more active and kept getting her arms and legs stuck between the rails. I think it depends on what type of cot you buy, if the rails are quite far apart then maybe it's better to have one. Although the padded bumpers look much nicer and cosier, I have seen mesh versions available which would prevent arms and legs getting stuck and allow more ventilation than conventional bumpers.