Which backing is best for linen crotch rip repair?

Hello everyone! I have 3 pairs of linen blend (85% Viscose, 15% linen) pants that have ripped in the crotch area, each slightly different. After researching, I think I know how to repair but I am confused on the backing part?

For the backing, is it best to use iron on interfacing or another piece of linen?

Does thread make a difference too (cotton vs polyester)?

I am brand new to sewing and honestly have no idea what I am doing but trying to figure it out.