For any Android users out there, the 3rd party keyboard SwiftKey just released version 5. It’s now free and supports Cymraeg. You can select up to 3 languages for auto-correct/auto-suggest.
A dedicated Welsh keyboard called LiteratIM is also available for Android. It has the advantages (for me) of including the single quote/apostrophe character in the main key set (other keyboards I’ve tried hide this away in the punctuation key set because it’s not as common in English), and you can type in an English word and the auto-suggest will come up with a Welsh suggestion.
https://play.google.com/store/apps/details?id=org.troi.literatim
I’ve always used SwiftKey and love it! I find it easy to use and all functions accessible, Iparticularly like having arrow keys available making it easy to navigate.
I’m not familiar with LiteratIM but would like to see how it works.
I’ve been using LiteratIM for a while now, but I’ve got to admit, I think Swipe might be my new favourite 
My go-to keyboard is the Hacker’s Keyboard…access to the full set of regular keyboard keys is indispensable…but I may try SwiftKey again if they’ve added arrow keys and more.
LITERATIM is awesome though. Wish I could combine them