Hi Kimberly:

How about:

RSVPdesignsbykim.com
kimsimplysaid.com
simplysaidbykim.com
loveletterdesigns.com
lovelyletters.com
kimsletters.com
invitationsbykim.com
RSVPinvitations.com

I have not checked these domains so I ma not sure whether they are available. I used Kim rather than Kimberly because you want to keep the name as short as possible. The shorter it is the easier it is for people to spell.

It can be hard to find a name so I feel for you :)

Hope some of these work out for you :)

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