For anyone else looking for them, I had some great help on here so just wanted to share where I eventually found them to help any mums who have arthritis or hand problems that make poppers a nightmare.
Right now they have some lovely packs of pjs in Tesco, some snuggle sleepsuits with zippers in Asda, there are some zipped sleepsuits in H&M in store not online unfortunately and not many and sadly you have to be lucky with sizing as they don't seem to hold stock and there is one zipped sleepsuit in Next for newborns. Mothercare also stock newborn pyjamas but they are very expensive compared to the supermarkets.
Hope this may have helped as I have been looking for months and finally they seem to be coming into stock.
can also suggest you take a look at zippy suits - they make baby sleepsuits with a zip along the leg. I love these and still haven't seen anything else like them. try looking online for them. poppers just drive me mad!
For newborns you can get baby nighties which dont have any poppers, they are sometimes also called bundlers. I have seen an increase in demand for these from grandmothers as it seems many of us used to be put in baby nighties when newborn/little as it made nappy changing easier in the night as not having to mess around with poppers, so I have started to stock some