Right around 3 months of age, most babies start trying to multi task while eating. A nursing necklace can help keep them occupied and latched on so you can get that feeding done with, nipples intact. I've seen Booby Beads and nursing necklaces for sale for as much as 20 dollars. Luckily, they are easy to make, even for the chronically craft-impaired–like me.
The lace I used was a few bucks for several meters, the beads are plain wood, and the ring at the end is the kind used for potholders. Everything involved is soft and completely safe for baby.