Cheap natural fibre sleeping bag?

I wanna get DD a nice sleeping bag but they are sooooooo expensive . I would like one made of cotton and/or merino, that's about the same warmth-ness as a standard weight gogo bag. Is there anything cheaper out there?

I was thinking maybe I could get a cheap one-layer cotton one from somewhere, and then somehow sew another layer or two of cotton or wool onto it to make it nice and warm... but I have no real experience with such things so don't know how/if that would work?? I have a few spare woolen blankets that I thought I might be able to cut up and sew onto a cheap cotton sleeping bag, but I don't know how the fabric works (can I just cut and sew or do I have to do something to stop ot fraying?) so don't really know if that'd work... Anyone have any ideas?

gogo bags are expensive but they last and wash and dry well (in the dryer too for fast turnaround if you need it). Sophie has had hers since she was 2 months and there is still room for growth - she is 20 months today (omg where did the time go ) Many other cheaper brands are sized so in that time you may go through 2 or 3.