A lovie or a comfort item is a great idea. It can be anything that the child can safely sleep with that brings them comfort. Touch, sight and smell are all important aspects of this. Common lovies are little blankets, soft toys, etc.
This must be distinguished from a ‘prop’. A prop is something the parent controls, and uses it to help the child sleep (i.e. breast feeding or rocking to sleep, or a toy that soothes baby but only the parent can operate). This often means having to go into the child during sleep when he wakes and can’t return to sleep without it, and so a pattern of disturbed sleep is established. A lovie is controlled by the child – a soft toy to cuddle, a blanket to rub against his cheek, etc.
By the way, a dummy (paci) can fall into either of these two categories – it just depends on how you use it!