That’s a lovely pattern for a fishtail. Why not use a pattern like the one you found earlier and substitute this stitch pattern for most of the body? When you get to the lower body decreases, change to stockinette stitch since the rapid decreases in most fishtails would disrupt this pattern.
Knitting a swatch will help you determine the size you get for the stitch pattern and then calculate the number of sts to cast on.