Also depends on your child's size as well.
With DD, I used Bumgenius OS (Version 1 or 2) Elastic has gone on 4/5 of the original 20. Got free replacement velcro tabs to sew on them by emailing UK arm of Bumgenius.
My DD used them daytime for 5 months and at night until 16 months and they fit her throughout. We moved DD to trainer pants at 5 months as we EC'd. (i.e. Offered her a potty from a young age, we do the same with DS)
I found wee nappies only need one 40c wash but poo nappies needed a couple of washes and/or a prewash. I only use Fairy non Bio Powder.
That said we only had poo in nappies until 10 months, so they did get much of a battering.
I liked them enough to buy a set of Version Three Bumgenius OS nappies for DS. What a mistake..he outgrew them at 5 months old !!! So I had to buy some MEOS and wraps for day time use and Quick Flip nappies for night, both of which have a bit of growing space for my baby boy.
Through he is on the 99.9% centile line in the red book in 1 year old clothing and was bigger than the 18 month old I met yeaterday (mind you he was a small 18 month old but still)
I would definately recommend quick flip's for night use and I really like motherease one size for day. Easy to wash/dry and mine have a stay dry inner layer so his skin stays dry.
HTH
I hope he will slim down when he getting the hang of crawling, else I have virtually new Bumgenius sat in the cupboard.