we had already decided we would order suntan lotion and baby milk to save on luggage weight but we hadn't even thought about ordering nappies from there!
But don't forget that you'll still only be allowed your standard hand baggage allowances and from memory the Thomas Cook one isn't generous. Do you really want to be loaded down with a pile of nappies as handluggage? Where are you going to? If it's somehwhere were you can buy nappies etc easily enough, I'd take just an initial supply and buy them once I arrive.
Given that you're only allowed 10kgs and it has to be only baby gear, if you are wanting to buy a good case that will be of use in the future, why not buy something decent that is the maximum standard size for handluggage, instead of buying a big case that will actually carry far more than that and weigh more in the first place? EasyJet, as well as most scheduled airlines will let you take on a case measuring 55x45x25 - as long as you buy a reasonably lightweight trolley case, that will come in at around 10kg once filled and will be of use fior many trips to come.
Also, bear in mind that a large, half empty case might attract attention from security and Customs. It has never happened to me but like many regular travellers to Cuba I always go out with far more than I come back with and one does hear stories of travellers leaving Cuba with empty cases being pulled over to explain what they've done with the original contents. Likewise, especially with large rigid cases that seem to be far bigger than the traveller actually needs, British Customs take an interest in what might be being concealed in the actual construction of the case. As my parents have got older they've learnt to travel lighter and lighter so that the luggage was easier to manage but found themselves also being pulled over for manual checks in the 'Green Channel' here and in the US the lining of one case was actually slit open during the security check. In the ned they bought new smaller cases that would get filled and had no more trouble.
SM