Do you RF ground your indoor miniwhip? A ground wire even to an outlet ground might help. I have done it before in a pinch for a temporary setup. Huge YMMV depending upon electrical system RFI.
Could you hang it from an eve or gutter? Snake some RG-179 or RG-316 through the window. I have done that with the coax under the closed window in a piece of un-shrunk heatshrink tubing to get a feedline outside.
I often use those inexpensive eBay 75-ohm "flat" coax jumpers under windows. Most are not really flat, but more like probably RG-179 or similar inside the casing. They are typically less than 1' long, so losses are no big deal at HF and lower.
Since the 31' vertical feedpoint is readily accessible, I intend to replace the 1:1 balun with another unun to flatten the multi-band impedance curve at the feedpoint at little. Balancing losses at the feedpoint versus losses in the feedline. Yeah, I know is not a big deal for receiving, but I do not mind experimenting a little with the deployment during cooler weather.
I was considering another basic 4:1 unun, but I kept thinking about what G8JNJ did after analyzing the Comet CHA-250B match.
https://www.g8jnj.net/cometcha250b.htmI considered building one, but then I stumbled across a similar dual-ferrite unun on eBay. :)
https://www.ebay.com/itm/303018040561It is a little different design, but the same idea. I am not entirely sure how it will fare under 80m, but "whatever" as long as S is decently over N considering the usual noise levels down there anyway. Either way it probably will perform no worse than a simple 4:1 unun, so again, a "whatever" for my purposes. Something different to try I suppose.
At some point I might try the even simplier G8JNJ approach to multiband vertical matching using a bifilar winding on an iron powder core. It is further down the previously linked page. I still have an S9v18 vertical in storage.