I used to make dolls and stuffed animals for my daughter, with matching clothing for both.
Back then, I'd glean patterns out of old craft magazines, then alter them to fit my notions, or design my own stuff. I made overalls, pants, dresses, bonnets, bloomers, hair accessories, etc.
My children started designing and sewing their own clothes and toys at five (daughter) and eight (son) years old, so wanted to make their own stuff.
But now you can download patterns and ideas from the internet to adapt to your needs.
You can buy dolls cheaply at resale places, on Craigslist, from big discount stores, etc.
Or just buy an off-brand doll that copies a popular doll.