@AderynOren
Macsen has an interesting history and legend behind it: www.britishbabynames.com/blog/2018/09/name-of-the-week-macsen.html
Alys is gorgeous. Fflur also gorgeous, but harder for non-Welsh speakers to pronounce. If you like Fflur, how about Ffion?
As Mike says, correcting your name gets tiresome. I usually give up after 2 or 3 attempts and accept my fate. Also, people can be very funny about being corrected. I had an unpleasant teacher who told me it was rude for children to correct how adults pronounce their name when I politely corrected her in class (first register). So I always feel awkward doing it! I can live with the mispronunciation but my Mam hates it. A colleague in my last job made the mistake of getting it wrong in the Cardiff office and was treated to a lecture on Welsh grammar 
@MikeUniformMike - if said name has an English equivalent beginning with the same letter that was popular in the 80s then you're right
Mam thought she had nailed 'Welsh name which will work in England', bless her.
@mamansnet - never heard of Glain before, but I like it. Tesni is gorgeous, I love the meaning as well.
I like Eleri. DH used to struggle not to say 'Ellerry' until DuoLingo introduced him to Eleri Lingo. Meleri reminds me of Malaria (by sight, not sound, also I have a strange mind so it's probably just me). Teleri is nice, but I worry her nickname would be Telly or TV (I knew a girl at school with a similar ish name this happened to).