Hi, I know this will not be for everyone, however, Amazon are matching quite a lot of the baby and kid events. Size 5 nappies are £13.33 for 144 which is cheap alone, however if you spend £25 or more with your American Express using code AMEX16SWP, they will give you £15 off. As a result you get 288 nappies for £11.65. You just need to use any amount of reward points so I used two and took 1p off the price and received the £15 saving.
I hope it helps someone. I think more nappy sizes are also on sale.