Our first born is [name_u]Hudson[/name_u] [name_m]Louis[/name_m].
The only name so far that my husband and I like (now that other names have been thrown out for various reasons) is [name_u]Mason[/name_u] [name_m]Kenneth[/name_m].
I don’t think they’re too matchy! When I read [name_u]Hudson[/name_u] and [name_u]Mason[/name_u] I thought “huh nice sib set”. I think they go really well together.
They’re slightly more matchy than I would ideally want, but not dealbreaker-level by any means, and they’re stylistically very cohesive! If [name_u]Mason[/name_u] is the only name you agree on, I say go for it.
Other non "-son" suggestions (hidden in case you're not interested!)