Excuse if this patterns a little hard to understand - I am by no means particularly competent in pattern writing, but I've given it my best shot. I've put together this design by merging a few other slipper patterns together, in an attempt to make a pair of slippers that are incredibly easy to make, and that require no sewing together at the end (as that's my least favourite bit).
This pattern makes slippers that'll fit an average female foot. However, it'd be quite simple to add length if needed in the rows just after the heel has been formed.
Suggested yarn: Sirdar - Denim Ultra (mega chunky with cotton and wool)
This yarn was nice to work with and washes easily, but to be honest, any nice chunky yarn will do the job. Otherwise,3 strands of worsted weight knitted together would be just as good. For the trim I used 1 strand of worsted weight yarn.
Needles: 4mm or US size 6, a set of 4mm circular needles, and a crochet hook size G
Tension: 10x10cm square = 12 stitches x 18 rows
Shaping the heel
CO 18sts
Knit in stocking stitch for 11 rows
p11, p2tog and turn
*k5, sl1 k1 psso, turn
p5, p2tog, turn
repeat from * till 6sts left on needle
Pick up 7sts along the left selvedge and knit them
Next row: p13, pick up 7 stitches along the right selvedge and purl them
You should now have 20sts
Continue to knit in stocking stitch till the piece measures 10cm from the back f the heel (I make this 9 rows).
Adding the strap
At the beginning of RS CO 10sts
Switch to circular needles, and knit 3 rounds.
Cast off 8sts in the middle of the strap
k1, kfb, knit to last 2sts, kfb, k1
(you can now switch back to straight needles)
Knit 4cm in stocking stitch (I make this 7 rows).
At the beginning of RS CO 4sts
The rest of the pattern is knitted in the round.
Here you want to place 7sts on 4 needles. Positioning the newly cast on 4sts next to 3sts from the other side of the slipper on the first needle, so the whole and the strap are in the centre.
Shaping the toe
Knit 3cm (5 rounds)
*sl1 k1 psso at beginning of 1st needle
Knit to 2sts at end of 2nd needle, k2tog
sl1 k1 psso at beginning of 3rd needle
Knit to 2sts at end of 4th needle, k2tog
Knit 1 round
repeat from * till 4sts left of each needle
sl1 k2 psso (double decrease) at beginning of 1st needle
Knit to 3sts at end of 2nd needle, k3tog
sl1 k2 pssoat beginning of 3rd needle
Knit to 3sts at end of 4th needle, k3tog
Cut yarn, and pull through the remaining 8sts and tidy away all loose ends.
You can finish off all the edges with a line of single crochet to make a trim.
Hope you enjoy the pattern :)