Don't know if you have seen these:
https://as-molds.com/the-bulletmold-foster/
Traditional Foster style or with specialty attached wad. These are full bore so eliminate wad fit issues.
I have not bought one so can't speak to quality but they are significantly less expensive than the "other" Russian slug moulds. I guess these are also heavier than you want.
They have a selection of other mould styles too and a relatively lightweight version of the Lyman sabot slug at just under 1 oz.
You may want to fill the cavity of your Mihec slugs with hot melt glue or silicone caulk... or something to help keep the skirt from collapsing and also to keep wads from blowing into the cavity.
Longbow