What TV tuner does your upstairs TV have currently? Is it DVB/Freeview or DVB-T/Freeview HD compatible?
You will need to add a HDMI modulator if you want to recreate your existing coax/magic eye setup with Sky Q. There are modulators that convert HDMI to an SD standard channel, and “better” models that will convert to a 1080p HD channel, but your TV needs to have an HD compatible digital tuner.
Some modulators also support magic eye control - they have an IR emitter that fires IR at the SkyQ box sensor as well as the receivers that go at the remote TV. If you pick a model without this support then you need a separate control solution.
Some modulators also include HDMI pass-thru, which means you can connect the Sky W box and local TV to the modulator directly and don’t need a separate HDMI splitter (as there is only a single output on the Sky box which needs to be connected to two devices).
A HD modulator with IR control and HDMI pass-thru built in can be found here:
Edision HDMI Modulator Xtend HDMI to DVB-T (HDMI Loop, RF Loop, Control Infrared Signal via Coaxial Cable, Plug & Play, Full HD, HDTV, DVB-T MPEG4, USB Pre-Config Function) Quick Installation
Edision HDMI Modulator Xtend HDMI to DVB-T Quick: Amazon.co.uk: Electronics
If you would like to be able to watch different Sky channels and recordings at bithbTVs at once then it would be simpler to sign up for multiroom and have a Sky Mini at the remote TV.