I am trying to spell my name in Irish, in a way that it still sounds the same as in Portuguese.

My name is Lívia, in English it would sound like LEE-vee-a, but in Portuguese the "i" sound is shorter, more like the "i" in "mint" than in the double "e" sound.

Those are the spellings I am trying out:

Líbhia (I think this would sound the closest)

Laoibhia

Laoibhe

And there also the "bh" and "mh" difference.. is there any?

I want to make a pendant with my name, and maybe a tatoo later on.

You can listen to your ideas here:

http://www.abair.tcd.ie/

I think the first would be closest.

(Personally, I don't think you should change it. V is used in Irish for some things)