There’s probably one out there somewhere but I couldn’t find a pattern for a flat circular pillow.

Here’s basically what I did:
Cast on 15 stitches with one strand of yarn.
Add second strand of yarn then K1, Kfb to the end.
Join and continue knitting with 2 strands for 6 rounds.
P 1 round.
K 3 rounds.
P 1 round.
Knit 5 rounds.
K1, K2tog to end of round.
Bind off using 1 strand of yarn.
Stuff with stuffing of your choice.
String end through bound off stitches and pull tight to close.
Weave in ends.
Embroider a smiley face and that it!