whatsapp with Italian number in American phone

Hi all, here' s the challenge:

I set up WhatsApp while in my country (Italy) on a Samsung S4, (Italian sim card and Italian phone number). I moved to the States for work and was able to keep my Italian number linked to WhatsApp: I simply got an American sim card.

Recently I got a new phone, Samsung S7, so I'm wondering if there's a way to "transfer" my chats from the S4 to the S7, while keeping my italian phone number linked to my account.

To add a layer of complexity the old S4 had a micro sim, while the S7 has a nano sim...

I add a look around but didn't find anything relevant

Thanks!