Just get an old AlphaSmart from eBay. I used one to write my last book and it worked very well - it isn't loud like a typewriter, and you have no distractions at all. They're also built to take a beating, so if you drop it, it's no big deal.

If anyone is interested, the book is called NSFW and it's my 3rd:

https://www.amazon.co.uk/NSFW-Other-Stories-Jamie-ONeill-ebook/dp/B0FHTBZ11Y/

Good luck with writing.