What to wear to Glyndebourne in v hot weather - £400 budget

[PapayaMarmalade]

I’m going to Glyndebourne next weekend and the forecast is HOT. We’ll be picnicking outside and I don’t have a thing to wear. Any suggestions? Budget up to £400, size UK 8-10

Are you all doing black tie?

I quite like this...

https://www.boden.com/products/women-tulle-bow-party-dress-vibrant-pink-d1553pnk?

Or this with matching top...

https://www.next.co.uk/style/su896376/y27529?

https://www.next.co.uk/style/su977563/g73692

Thank you! We are all doing black tie.
The Boden one is a probably a bit fussy for my taste. The Next one actually looks beautiful but it’s 100% polyester and I think will be too sweaty.

I like this

https://www.next.co.uk/style/SV086106/G30197

Viscose...

https://www.next.co.uk/style/sv104885/v89981