Is the bolster connected to the chair cover or separate?
A bolster would be a tube of fabric with circles sewn on the end. Are you planning on piping? I like to mark the seam allowance and stitch a row of stay stitching first. Then cut with small slits. It's easy to plan out on paper. Write the measurements and add in the seam allowance on each end.
When you sew curves try to pull the fabric so it is almost straight going into the needle plate.
https://www.youtube.com/watch?v=HTOGt4cRdJE
Double welt cording isn't hard either. Here is the one I use.
How To: Make Double Welt Cord » Curbly | DIY Design Community