Help needed, making an armhole (sewing)

[SilverHawk]

I'm making Butterick 6064 in quite a loose, woolly tweed material and there is no way I could use it for the armhole bias. It's too loosely woven, although woolly. Could I use commercial bias binding (am worried it will be too thin), or fake leather (don't really want to)?
What could I use?
Any ideas, however strange ?

What about a close-knit wool in a complementary or contrasting colour?

Or could you back the main fabric with a medium-weight iron-on interfacing to give it a bit more structure? And then cut your bias binding pieces from that?

regular bias should be ok in controling the arm holes, have you stay stitched the arm holes?

Thank you flighty, you have two great ideas :)
Yes , I could certainly use iron-on. Never thought of that! I will give it a try tomorrow. It's quite lumpy and sluby so may not work.
I thought about a knit but didn't know what to chop up! An old t-shirt would be too thin.

No need to stay stitch as there are no sleeves.
I'm just trying to work out what to use for a good finish to the arm holes.
The material can't be too flimsy as the garment has a stay along the shoulders.

Could you face your arm
Holes instead of binding them? Or use normal binding but fold it all under inside so non is showing if you don't like the look of it?

Hello, are you Laurasmum as was? you were doing loads of that Disney stuff? Yep, I could do either but I still don't know what to use atm.
I will try regular bias on some scraps and the iron-on tomorrow. Can but try!
I just thought that the pattern would look so good as a cross between a gillet and poncho!