Best uniform white polos?

[HappyPalaces]

My Y5 daughter will need white polos for school uniform next year. Can anyone tell me which brands are particularly good/bad? I'm looking for ones that are opaque, soft (she's very sensitive to fabrics), and wash well. Any ideas? I live fairly centrally in London, so it's not easy to just pop out to all the big stores and compare. I assume I'll end up buying a few different ones online, but I'd love some suggestions.

M&S

I found that Sainsbury's polos were softer and washed better than M&S. The quality of M&S polos went massively downhill between DS1 now 24 and DS2 now 14.
I always bought M&S, but was given some Sainsbury's ones from a friend with a daughter who has sensitive skin and will only wear soft clothes. They washed and tumble dryed really well.

Yes, I'm a bit iffy on M&S these days. I bought my older DD shirts, skirts, and jumpers from M&S for secondary and they didn't seem great. I bought some Tu ones as well and DD preferred those for all things, so I returned the M&S ones and saved a load of money!

I think I'll give the Tu ones a go for the polos.

I can't edit to add a second question, but has anyone tried those twofer dresses that look like a polo top and a skirt bottom? I wonder if those may also be more comfortable for my daughter and look neater, but not sure if there are any potential issues I'm not thinking of.

Sainsbury for polos, especially the ones that have some kind of magical stay white stuff in them. Their Summer dresses wash well too.

The Tu shirts also fitted DD better- we found the M&S ones a bit baggy. The Tu uniform is really good value (and lasts) in general.

I would avoid the split dresses- one bot inevitably shrinks or gets very dirty/stained, and you're out a whole outfit rather than just one piece... (unless it's just my child.....)

Tu or Asda are both the best ones we've had. Wash separately in bio powder and they'll be white at the end of the year.