When I made the jellyfish for the Supercute Sea Creatures, I used a single line of blanket stitch along the bottom edge.

My blanket stitch tutorial only showed how to do blanket stitch if you were going all the way around.  I added a little section to the tutorial that shows you how to start a blanket stitch if you don't intend on meeting back up with the first stitch so you can keep your first stitch vertical.

That tutorial page is WAY long.  It's such a monster.  I need to rethink that page and get it looking more usable.  Maybe I should split all the little bits up and put them on their own pages.  Hmmm.