Adams Architectural Woodworks makes great wooden storms.

You could find a local firm to make wooden storms.

You could make wooden storms yourselves.

And, if you make windows, you can reuse the wavy glass that you already have.

Thank you for these ideas. I wonder whether there is a high=quality, attractive low-E/high-R exterior fixed storm window, ideally wooden but clad for low maintenance, that has a removable panel to switch in a screen panel in summer? That would have the advantage of protecting the (restored) old wooden 6x9 sash, and on lower floors would enhance security -- it might be possible to specify whether an upper or lower panel is removable in the fixed storm, for security reasons, too. Then downstairs windows could be opened from the top for better ventilation of hotter air.