I would,as it gives the fabric more body,and it makes it hold up better,when you are working with the corners/points etc.I've made hundreds of dolls over the years out of many different fabrics,and I almost always use ,the appropriate interfacing.Just be super careful when ironing the interfacing on,that your iron is not too hot.
Kathi

Thank you so much Kathie! Could you recommend an "appropriate" interfacing?

You want a light to medium Stretch Fusible interfacing.
Kathi

You can try a sample and see if you like the outcome. Look for tricot. It will alter both the hand and the stretchiness of the fabric.

Thanks Kathi & Annie! I purchased some on a bolt, but haven't tried it yet. It looks like it will work just how I want it to though!

I made many cabbage patch dolls at a time when you couldn't find them I used a beige jersey type knit and never lined them they are still going strong 25-30 years later