Hi All 
I was wondering if someone is able to help me on something please,
I am confused to why, I think you’re doing very well translates to Dw i’n meddwl bo’ ti’n gwneud yn dda iawn … specifically I am confused on where the bo’ comes into the sentence, I would have expected it to be Dw i’n meddwl ti’n gwneud yn dda iawn
Thanks,
Lucy 
The ‘bo’ is the ‘that’ that tends to drop out of English sentences but needs to be in Welsh ones - “I think [that] you’re doing very well”
Siaron’s already given one perfectly good answer, but here’s another one (feel free to ignore).
If you did it with “I” instead of “you”, then “I am doing very well” would be Dw i’n gwneud yn dda iawn. When you add an “I think that” on the front, the Welsh changes dw i to bo’ fi - Dw i’n meddwl bo’ fi’n gwneud yn dda iawn. Because the bo’ goes where we can put “that” in the English, we tend to think of it as “that”, but it’s really “to be” - Welsh says “I think me to be doing really well.”
It’s the same thing with ti, except that people usually miss the verb out of the basic sentence that you start with. It’s ‘supposed’ to be Wyt ti’n gwneud yn dda iawn (or Rwyt ti in more literary Welsh) - and, just like with dw i, when we stick “I think” on the front, we drop the beginning of the sentence and swap it for bo’ ti.
But the thing is, wyt ti is exactly what you’d say if you were asking a question - so, perhaps for that reason, when people are making a statement they usually just start with ti’n (in the same way as people passing in the street will say in English “Alright?” rather than “Are you all right?”) - Ti’n gwneud yn dda iawn. So that means that it feels like you’ve had to add an extra word in, when you say bo’ - but without it, it’d be like saying “I think you doing well.” It’s understandable, but it’s not right!
Thank you so much Siaron
Thank you so much Richard - this is really helpful 
I’ve only just seen this post, the same thing drove me mad, it took ages to sink in!