Working with double-layered fabric

Good morning, everyone
I have a (maybe silly) question. I’d like to sew a jacket, but unfortunately the fabric I have in mind isn’t thick enough. Could I just use another fabric with it and basically treat the two layers of fabric as one?
I’m afraid I’m not skilled enough yet to sew in a lining.
I’d appreciate any help.
iris

You can do that. But to prevent it from warping while sewing, I’d iron the two fabrics together using fusible interfacing 

Thanks so much for the info—I’ve been Googling for hours and couldn’t find anything on this.
Best regards, Iris 

It would be better if you sewed the jacket twice and then sewed the two pieces together and turned them right side out, because using this double-sided fusible web (Flisofix) makes the fabric quite stiff and hard. But when you sew and turn it, it stays as supple as it originally was. That’s how I would do it

I’m afraid I’m not that skilled yet, and I’m worried I’ll ruin the nice fabric 

There’s another way to combine both fabrics into a jacket: sew them separately first, then put them together with the wrong sides together so that both outer sides show the right side of the fabric. Pin them securely together and sew a bias strip all the way around to join them. That way, you’ll achieve the same result without having to turn it too much and without using glued-together fabric, which isn’t exactly ideal.
With this method, though, you have to pin closely along the cut edges you want to join so it doesn’t fray. But if you lay it out neatly on a table, it should work well—then join it with the bias strip.

Thanks so much for the tip. I think I’ll try that out on a test piece. 

One more question: Should both pieces be sewn in the same size, or would I need to make the inner jacket a bit smaller so it doesn’t bunch up?
Best regards, Iris 

No, they should be sewn to fit exactly; otherwise, it’ll pinch or bunch up exactly where it’s most annoying. If you slide the sleeves inside each other and only have about 5 mm of wiggle room, it won’t fit anymore—so when they’re nested inside each other, they shouldn’t have much leeway.

Thank you so much for your help 

Sure :-)