I don't comp feed per se and I certainly don't do it for weight or lack of supply issues. More sanity issues, but I do give dd 1 and sometimes 2 bottles a day. I have since she was about 2 months old. I haven't noticed any real affect on my supply at all. I make enough milk to suit all her other feeds so it works for us. But it won't work for everyone I know. The only way I can get through breastfeeding is to offer a bottle or 2 a day. Otherwise I wouldn't be doing it at all. We're 7 months in and going strong with boobie and formula and this way she remains my longest breastfeeding bubba. DD goes between both easily without any drama and see's both boob and bottle as food. It works for us. That being said it doesn't work for everyone. As MadB said you can always trial it and you can always rebuild up your supply if it doesn't go to plan.