Yes, there are many bottle teats and you can increase the teat size as your baby grows and perhaps is unsatisfied with the slower flow of a smaller teat.

BUT

You don't need to change teats (or even bottle sizes) if you don't want to.

The 5 month old twins I was with at the weekend are still using their tiny newborn 50ml Sterifeed bottles at each feed. Of course they drink more than 50ml at a feed, but we make the larger quantity in a standard 260ml Mam bottle (that's for both of them by the way...130 each) and then decant it in 50ml increments.

This is working for everyone, so why change it! Plus, it encourages a more paced feeding approach, with the babies able to pause and identify after each 50ml how hungry they still are!

Do what works for you and your babies!