I'm using pigeon ppsu n pp feeding bottles. For those who use the above materials.. how often do u change the bottles as well as the teats

For ppsu the bottles can last a year while pp bottles last half a year. For the teats have to change every six months. Btw curious what size teats are your babies using? My gal is 11mo and I am still on S size teats because she sucks very hard. But recently found that she is losing bit interest in milk, not sure if I should use M size