Seaming for sweater in stockinette and seed

I just finished a baby sweater that is done in stockinette stitch on the body and seed stitch for the arms. When I seam up the sides, which method should I use? Can I use mattress stitch for the side and backstitch for the arms or should I use all backstitch? Thanks!!!:cheering:

Here is a link to a whole online book about knitting that has some pretty good stuff about seams. This is alink to the table of contents. Read through chapters 21 and 22 and see if there isn’t something that helps. I don’t recommend a backstitch seam.