I'm not an expert, but I have a rocket oven, so I'll tell you what I saw go into it.
(I have the one that Tyler Morrison made in the video! You can watch my painfully slow process in finishing it here!
https://permies.com/t/90413/quest-beautiful-rocket-oven#748081 )
You want the one inch ceramic fiber board, and I think that's the higher temp rating as well. The rocket oven takes 1.5 sheets, so I'd say if you're going to make two rockety things you should buy 3 sheets. If you go here:
http://walkerstoves.com/index.html and scroll down, you'll see the J-tube plan that is used in the rocket oven video.
Have you got access to the microdocumentary here?
https://permies.com/t/rocket-ovens I recommend watching, because Tyler talks about tools and materials you need to build a rocket oven.
The firebricks in my rocket oven are half thickness and used as an inside liner for where the wood goes in. I think the sizing is pretty standard on those - there are half thickness and full thickness fire bricks.
Mineral wool, or rock wool, is used for attic insulation and every time I've seen it it's been the same thickness.