Oh dear !
Back to back wifi repeaters are a no-no due to halving the available bandwidth, you suggest AV plugs are unaccceptable, and there is no way I can install any cables on the ground floor.
My house is ancient with solid brick floors, and brick & flint walls, generally no carpets & no skirting boards on the ground floor.
I think I am going to have to go for the "least bad solution", which I assume is AV plugs. Happily my home is fairly remote & I know all the neighbours and there are no amateur radio enthuiasts within at least .5 mile.
Just to rule out any potential confusion, I'm not suggesting back-to-back wifi repeaters, just access points connected back to the router via ethernet cabling.
Until recently I lived in a property very similar to yours, and did just that; flat cable from the router upstairs to a switch (for my desktop stuff) and from switch to a TPLink 300mbit AP. A second cabel ran from router to a switch in the front room, for the TV, HTPC and other home AV stuff.
Perhaps round cable running along the floor in the corner between floor and wall?
You correctly state that back-to-back wifi halves bandwidth, you are aware that the bandwidth of home AV networking is half the stated speed, aren't you? ie, a 300Mbps home AV only offers a maximum[/] bandwidth of 150Mbps... and that is subject to wiring. Oh, it is a shared medium, too... be wary if you have more than one device attached to each access point and powered on...
The views expressed here are mine alone, and do NOT reflect those of my employer, present or previous.