Thanks for your replies,
@Greybird @b15erk and
@Elnnina , all very useful. I have actually sewed quite a bit using stretch fabrics and have mostly used a zigzag as I have had straight stitch seams break, maybe I’m tougher on my clothes than you all are! 😉 I hate using the lightning stitch though due to the difficulty in unpicking it.
One thing to be aware of on this subject is that Gutermann have introduced a new thread called the Maraflex which you can sew a straight seam with, I’ve yet to try it out. It is a bit more expensive that their standard thread at £3.15 for 150m compared to £2.15 for 100m of sew-all thread. Obviously a straight stitch takes less thread though than a zigzag so it should balance out. It’s on my shopping list for the next stretch fabric project so I’ll try that out and report back!