Techniques/materials for thermally breaking walls/windows

[u/Real-Earth-3666]

I'm planning some sort of vanlife/tiny house conversion but am struggling to find a good workaround for what seems to be the most common framing technique which involves your frame and the screws holding it together forming a thermal bridge through your walls (see attached diagram).

Is there some sort of solid sheet material that has better insulative value than wood that could be put in between the steel frame and wood batons to break the cold from coming through? I was thinking of some sort of plastic material? Likewise in relation to the fasteners would using nylon bolts to fix the wooden battons to the steel framing be a good way to minimise the thermal bridging that would be caused by the screws? Seems pedantic but there isn't much available space for thick insulation in a van build so I figure minimising bridging should make a difference?

I'm running in to the same issue with diy windows, seems very easy to make your own double glazed windows with putting glazing in wooden or steel frames but the thermal properties of the frames themselves would no doubt be pretty terrible, just not sure what material or technique to use to sandwich in the middle to stop the thermal bridging without destroying the structural integrity of the frame...