I kind of like this one...nice choice.
I have simplified the construction a little because I think it flows better (and the fewer the number of times they have to stick the needle in you!)
Instead of "One life no regrets" I have transformed it to "Life without regret":
Vita Sine Paenitentia
The reason I changed it (besides saving ink!) is because unless you really want to emphasize "one", Vita by itself implies "a life" or just "life" without further qualification. If you really wanted to you could add in front of it "Una" or "Unica" to emphasize one/single/unique...but as I said I think the construction above is best (especially since Paenitentia is such a long word.
A word of note though, the word Paenitentia, which means regret, kind of implies regret for a wrongdoing (you can actually see the modern word penitence evolves from the Latin form here) as opposed to say just regret for one's choices in general, which I gather is the theme you are aiming for. Unfortunately, I cannot find another form of regret that is different. This is a common problem in Latin. We just ran into it earlier this week with the word for pride, which also implies someting negative. In all cases, I wouldn't worry about it for the theme of your tattoo all that much, I just wanted to let you know.
I hope this helps, and with all my suggestions...get a second opinion here before committing to skin!
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Edit: I forgot to address the translation you suggested. The definition that I have for desiderium is desire/longing/want/requirement; desire/grief/regret for dead/absent/loss. I'm not sure that is the definition of regret that you are looking for. Using nulla is fine I think, but if you do use desiderium you would have to change nulla to nullum since desiderium is a neuter noun, it needs the neuter form of the adjective.
-Severus
