hard to find non-reflective, non-metallic insulating sheets. first maybe start with a floor covering and then shades. wallrock thermal liner not available in the us; maybe wallrock fibreliner?
acoustic paint for ceiling; thermal paint (maybe multiple coats?) for the walls. curtains? rug? interlocking foam tiles. works, 24 sq. ft. for like $25.
OK: two coats insulating paint. (then acoustic paint?) foam tiles or carpet on floor. (ratty one from basement?) curtains.