I think
Ernestine is a good name, although I consider it as old-fashioned, regarding the current naming trend in the US. But I have been enamored of
Earnestine lately, I find it looks more complete with the additional letter -a-.
Since you have mentioned
Thomasina, I think that's a good one too, but I would prefer Thomasin.
Greetings from 15 hours ahead!