I have an old door at the ground level which has a this window insert consisting of a bunch of glass panels that can be all turned with a handle (see photo). Needless to say, it does not provide good insulation. Rather than replacing the whole door which is overall in a pretty decent shape, I want to replace this old window insert with a regular window that is well insulated. Can you recommend what sort of window I should pick? I am not sure what the exact size of the opening is but the insert measures about 21" wide by 33" high. I want it to be clear. Thank you!