Hi there,
SO I was faced with a similar issue,
My patented Device uses an Nrf52840 in it’s design.
I chose the Hybrid approach, I made a PCB and Used a Xiao instead of reinventing the Wheel when the work was already done. With the proper planning and scheduling Seeed Studio can supply what you need. It is up to 
however to Plan properly, the old adage " Fail to Plan , Then… PLAN to FAIL!" 
Applies 
In your situation the Cheapness of the chips already , then in Quantity it’s a NO brainer. IMO. Check out the first revision of the PCB, I’m at REV 6, now and the polish is ON!
Man it is Sweet, This stuff goes together better than Peanut Butter and Jelly or Cake & Ice-Cream ! 
HTH
GL 
PJ 
Battery Power went from 1 day to 27 days for example… The Certifications Seeed has for FCC part 15 Class B devices was a feather in the Cap. BTW! By making No changes to the Radio or RF section the Certs apply. 