you don't actually need a smartphone at all. i discovered this by accident when my smartphone died. here is what i did.

  - installed the whatsapp "app" on my crappy old android tablet that i hardly ever use
  - used SMS to my dumbphone to link the installed app to my phone number
  - opened "web.whatsapp.com" on my laptop browser
  - scanned the QR code in the android app to link the browser session to my account

so, i am now happily using web.whatsapp.com in my laptop browser day to day and all i needed was a crappy android tablet and a dumbphone to set it up.

i have been using web.whatsapp.com on laptop for long time - pretty sure it's 3-4 years at this stage. maybe i am wrong on that.

i also find the browser/laptop whatsapp much nicer to use - copying/pasting etc. is so much easier than a smartphone, for me at least.