Silver Rose, now this might be too late for the current dress, but on your new machine do you have a triple straight stitch, this is a straight stitch stitched in such a way that it has give and saves seams popping, so the stitch is formed one forward and then goes back over itself and then comes forward again before moving on to do that all over again. If you have this stitch do try it out before hand and see what you think. I use this stitch for armholes and crotch seams and they never pop. I have this stitch on my 1975 Elna SU and thus it is an automatic smallish stitch that cannot be elongated, but today's newer machines may well have this stitch and it may be able to have different lengths. If you have this stitch and use it, and then want to unpick may I warn you that this is a stinker to unpick you are likely to end up with holes. I learnt the hard way and decided to sew every seam on a pair of trousers with this stitch, and then found the trousers were far too big and in order to save them I had to clip each and every stitch very carefully but this took several days as it was so intense trying to be careful. Good luck.