At the risk of being exceptionally contrary, I don't like the flats either, as Elle pointed out the proportions are off, they may actually work on someone with giant feet who would never wear pointed flats for fear of them looking like skis.
Not a fan of micro flesh coloured fishnets either, whenever I see them I actually mistake them for a skin disease instead. If it's your thing to be a bit more quirky/fun with your style I'd say go mad with the fantasy tights, sheer coloured numbers with polka dots, interesting patterns, etc. Keep the top simple and similar in tone and wear with demure brogues like the Bobbies to tone it down a bit and make it less party wear. If you want boring sheers, Falke does a couple of 8 or 12 deniers that even out and disguise reasonably well without reading as tights as they have a very wide colour range and I'm told they last a fair bit longer than most low denier tights, they're a stewardess staple.
Trolley, it's a crying shame to cover up that dress with anything. Unless you're exceptionally cold blooded I think it's madness to be shopping for anything on top as you're just going to run into fit issues and different hem lengths that don't match up. Best to just face that there's going to be a brief moment where you're going to look a bit of a tit between venues and buy a coat that actually works in the rest of your wardrobe without all these extra demands because short of finding some fantastic cape or opera coat I struggle to think of anything that will go with it effortlessly. Maybe an oversized silk knit heavy weight scarf, but those will probably set you back more than a jacket. If by some miracle you are effortlessly cool enough to carry it off, a denim jacket could potentially work in a just got my casual jacket on over my frock kind of way.
When you tried it with a men's blazer did you stick your arms through? I'd just wear it on the shoulders only.