Tickets for JR central online?

Hi guys,

I'm planning ahead for our trip to Japan in August, and I was wondering where I could book tickets online for JR central lines (Nanki, Hida). Since we'll be there during Obon, I've been told to book train tickets beforehand for the biggest journeys. I've been able to find out how to book/use SmartEX and JR-west tickets, but I can't seem to find the 'official' place to book JR central tickets. Are websites like Navitime or Klook a good bet for this? Or should I just buy them on the spot?

Thanks!