Best to do a swatch with double strands of the lighter weight and see how it compares to your swatch with a single strand of the heavier one.
What are you making? There are times when thinner yarns are used in striping and, instead of doubling, you can work increases across to bring the number of sts up to where the lighter weight yarn is now as dense as the heavier one AND worked on smaller ndls. If working back to the heavier one, you'd then reduce the st count back to the gauge for the bulkier yarn and return to using the larger ndls for that yarn.
Something like this: