converting tension?

[ideefix]

I found a very simple pattern for a V-neck vest. However it is for a thick thread ( tension 20 St) I would like to use a mercerized cotton, tension 24 st) Is there a way to convert the pattern ?
I have looked everywhere for a pattern that would go with this tension but no luck, and larger needles give a fishnet effect. Not nice.

Good advice would be welcome

Thanks