I think any daff would do, however I would ask what the colour scheme, overall look is as a standard daff can be really bright, and on photos can just look like a yellow/orangey blob against a wedding suit.

There is a variety of daff called "irene copeland" i think which is more like a peony and gives an excellent main flowers with a few smaller daffs around it (nice one is called "bridal crown")

There are loads of variations on the standard daff - it might be nice to try something a bit different, but still in keeping with the welsh theme??

I love daffs