Baby Socks or booties

I am wondering is are all booties that are knit in the round done by knitting the instep flat like you do the heel of a sock? Can you make booties more like you do socks?

And are there baby socks that anyone has made that use a thick yarn to keep the baby’s feet warm without shoes?

Some easy booties here worked differently. (also check that site for lots of other good patterns. )
Or thicker weight baby socks

Thicker yarn worked to a tighter gauge than usual would be warmer.

I think I’ll start with those first set of socks… Thanks!