Whatsapp back-up SOS!

Hello! Can anyone advise how I can switch WhatsApp to my new iPhone 11 without losing data/conversations?

My issue is that I don't have enough memory on the phone X to back it up WhatsApp without deleting loads of videos/images. Which I need for work. Happy to buy WhatsApp storage but not sure if that's possible.

iPhone X 62.2 of 64gb used

iPhone 11 - 52 of 256gb used

Issue 2... I've built up so much content on the iPhone 11 now and I'm unsure if syncing one phone to my iCloud will wipe the other?!

I don't think I'm a complete technophobe, but can't work out how to do this!

Any help much appreciated, Ric.