Need help with newborn sizing!

Going to be a FTM and I was thinking to start shopping for the baby. I am really confused with the sizing. H&M has sizing starting from 0-1month, while M&S has 0-3 months, while Mothercare has a newborn sizing which I guess will only work for a month. I know newborns outgrow their size very quickly so I don't want to buy a lot of clothes. Kindly suggest as to how many bodysuits, sleep suits I need for initial month? Also, should I stick to 0-1 month sizing?

Also, any other brands that I can check out for clothing?