Are you in France? I'd be tempted to look at Breton names. They'll be a bit of nod to your celtic background and will work better. Some of the names are delightful. Some like Yvan are very similar to the welsh versions.
What I mean by not travel is that they will be met with confusion. The tendency is to find the nearest name they know or have a stab at it, or a refusal to use it and just use something else.
An example would be Geraint. You'll get Jeraint, Guh-rant, Grant ...Er WTF
Gwenllian will be Gwenthly-ann, Gwenlillian, Gwenli-un or I'm not even going to try to say that, and worse
Mair will be Mare or Maia
Meinir - My-nur or Men-ee-ur
Llinos - Clee-nose
The child will get this almost daily. Sometimes several times a day.
You can try to teach people but it will get tiresome after the first few hundred times.
I would use a welsh middle name. Fflur and Glain stand out as my current favourites. Haf is a filler middle name.
Some of the names will work in France and whereas they might not work in England or Scotland, they'll be lovely in a french accent. I think Luc is nice, Fflur will sound ok (they'll say Fleur). Gethin is fine in England but won't work in France. Manon is a name in France and Wales.
If your family has a broad welsh accent - I'd consider how the name will sound back home. I wanted Mary for a DD (I know but as much as I love the name Mair, it wouldn't work down here) but it would have been 'Merry' back home.