How do I extend my 6-week program?

I run a 6-week private coaching program for postpartum mommas looking to lose weight and balance a fit lifestyle with their new-baby-routine. During the 6-weeks we focus a lot on mindset, setting appropriate goals, etc. We do get into an exercise plan and diet (I’m also a personal trainer), but we barely scratch the surface on these things.
Question is – I am considering offering an additional 4 or 6-week program to the clients who have already completed the life coaching program, that focuses MORE on the diet and exercise portion. I don’t envision the program being as time intensive (for me) as much of it could be automated.
I currently charge $600 for my 6-week program, and am thinking clients can choose to “extend” their coaching package by enrolling in this course for…$300? $250?
I don’t know how to price this “extension” program, or even what to call it!!
Any tips, guidance or resources you could point me to?
Thanks tons!