New iphone / Back up issues - Not space on old iphone HELP!

Hello,

Having a nightmare trying to get my whatsapp onto my new iphone. I don't have any space left on my old iphone to back up my videos/photos, which i would like to keep or download to a PC.I have downloaded everything i don't use already to make space but it is like a drop in the ocean.

I have tried exporting chats but they are too big and even with maildrop, just crash/don't send.
I have tried to use software but can only find ones that i need to pay for and tbh I would like to avoid this if at all possible.
Can't use icloud or itunes as i need to backup my whatsapp first which i am not able to do.

Does anyone know any other options or any FREE & SAFE/RELIABLE software i could use?
I am going on holiday tomorrow and would really like not to have to take two phone with me :(

Thanks in advance!