Hearth Options on Uneven Floorboards

[Pib]

Hi I’m Liz, and this is my first forum post anywhere, ever.
I’ve recently removed an old gas heater in my home, restored the tapestry brick fireplace, restored a woodfire heater to fit and since have had it installed. While I’m finishing off the wall plaster and skirting, I am faced with my next challenge: the hearth.
The house was built in 1947 and while it’s been restumped, the floorboards here are not level. I plan to restore the entire room once the walls are complete and painted.
The left side of the base of the heater fascia sits 40mm above the boards, while the right side sits 45mm.
I’ve watched some youtube videos, and based on what I’ve seen I’ve thought the way to go might be to install a temporary frame, fill the gaps with the foam stuff, cut excess foam, then pour self levelling concrete into frame, leaving enough space to install tiles to sit flush under the heater fascia.
Or is the angle minimal enough that I should plane the boards so that they’re level, and then install cement boards and bring up the base to sit flush under the fascia then tile them?
I’ve read some posts and I see people talking about allowances for board movement, which I’m not sure how to consider in my approach to my hearth.
I’ll appreciate any advice or direction, I’ve never done anything like this before, feeling a bit stuck and would just love to progress this so I can have a liveable dining space and lounge room (especially for my cats), it’s felt a little overwhelming and I’m not sure who to even call. Happy to answer any questions that might help get the right advice.
Thanks so much in advance.

 

[stovelark]

So for the hearth, 40MM is roughly 1.5 inches. Maybe a nice slab of bluestone or something decorative for hearth protection? Even an 18x48 hearth extension might fit nicely under the insert edging. Looks like adjustable levelers under the lip too? A lot of choices to do, depends on your effort and/or budget. Good luck with it- Hope the insert has a liner up the chimney flue? What insert is that? Looks nice against the brick background.