These kinds of mutations are very much a moveable feast, and you can get away with all sorts of stuff. My aversion to h's are rightly mentioned - ei enw hi (or possibly ei enw 'i even) is totally natural to me, even though I am growing an h in places since moving westwards.
But in the norht you will hear things like "ei mham hi", with the h inserted into the word mam: totally against any known grammar "rule", but a totally natural part of some people's speech.
In other words - mutations smutations. Stop worrying about them, and use what feels right. You will very quickly find that you either fit in with the Welsh that you hear most, or you'll forget to mutate / over mutate as much as a natural Welsh speaker does. Either way is fine!