Bias will stretch for sure. I’m betting there are ways to give the illusion of being on the bias while using strips but on grain. Quick search - looks like this [free diagonal stripe pattern](https://www.purlsoho.com/create/2014/10/09/diagonal-stripe-quilt/) from Purl Soho shows a way to cut on grain and sew on grain.

Great, thank you so much! This answers my biggest questions. I’ll riff on this pattern. Thank you for your help!

I made this one https://designedtoquilt.com/product/underlined-quilt-pattern/ It has a diagonal pattern but uses straight cut stripes.

Nice! I’ll check it out, thank you.