@harribot
It's incredibly easy.
You crochet a circle the size you want the bottom to be. The first bed I did in all uk dc. The second was mostly half trebles.
For this one, I made a circle 18 inches in diameter using 3 strands. I made it this size to suit my brothers big kitty but whatever size you want.
Then you do a row of back loop only to create a hinge, and stop the increases and just make it a continuous tube. I did this until the side was around 7 inches. You then fold the side over over to meet the other half of that stitch and do about 10-15 slip stitches, then I stuffed it with cut material. Do more stitches, stuff etc until you finish.
I added a catnip pocket to this one too. I've some pictures and a YouTube link I followed.
Here are pictures
imgur.com/a/litFlFb
there's a pic in here of it being joined imgur.com/a/uHcDwSE
Ziva lay in it as i was stitching it ♥
I preferred the stitch side down but when you get to the hinge part just look at both sides and decide which you want facing up. It's really incredibly easy. I'll be here if you need help. The cats loved it .
Video
this little trick helped me make a ball of wool of all my scraps hence the colour changes. No ends to sew in, amazing!!!