The fantastic Sophie of Ada Spragg posted in her Instagram stories last year about using two threads as an alternative to top stitching thread. I’ve employed the trick on a few pairs of pants since and have been delighted with the results.
Simply thread the machine as normal and put both threads through the needle. If you don’t have two spools of the same color thread, you can wind two bobbins and use one of them in place of the second spool.
Play around with the tension and stitch length on some scrap fabric until the stitches are just right.