I had the same dilemma.
When I switched to Samsung, I kept my Lumia 950 for about 8 months just to keep using WhatsApp without losing my chats. I did try few different methods I found but none of them worked, until I found WinWazzapMigrator in a forum. It worked perfect and they have step by step instructions (only a couple of minor things that you have to figure out, but their customer service is quick). The best $6 I had spent for an app (the only app that I had pay for that I am really happy paying for). Now my L950 is in the antique drawer.
They have two versions of the app: One for Android and the other for iPhone. Make sure you choose the right one for you.
Try it, you won't regretted.