Tell me about Boots, I've not really used them so far? How many points do you collect on formula?
Asda, Tesco and Sainsburys (and I think Boots) do baby events every 4 months or so I think, someone correct me. Nappies, wipes, bath products etc all go on offer, I personally think Asda are the best and put other things on offer too. Have bought door bouncer, inflatable ring and stair gates all from Asda baby event.
I also signed up to Huggies and Pampers online, they gave me free vouchers. Wait until the nappies are on offer and then use the vouchers. I saved mine, Huggies were reduced down to £3.38 for 36 nappies, I used £3 off voucher they gave me and got them for 38p. Emma's diary is a good site too as they tell you about lots of offers. I also use Amazon's subscribe and save for nappies, wipes and formula. Nappies are usually cheapest on Amazon unless their is a baby event on elsewhere. When a baby event starts stock up!! If you overbuy nappies you can swap them for another size.
I'm also a nappy tart and although DD mainly lives in branded nappies if there is nothing on offer then I will buy cheaper, Asda Little Angels are very good, as are Aldi nappies. Believe it or not Aldi nappies actually get a big thumbs up from lots of mums!
My tip to you is to keep all of your vouchers together (you will get loads) and then dig them out when you go shopping, just remember to check the date!