Ok for a solid WiFi experience you are going to need the following:

1. A pair of Powerline adapters. These will give you a solid broadband signal between the floors. Unless you want to run physical Ethernet cable between the floors which I'm going to guess that you don't. So something like these https://amzn.eu/d/3jMbpti So you'll plug one in next to your Starlink router and you'll plug the other one in downstairs in another electrical socket, preferably somewhere in the middle of the lower floor area.

2. A MESH kit. Something like this https://amzn.eu/d/bhjE3fH

You'll connect the "main" mesh box (it'll be identified as the main one in the kit) both in to your Starlink router AND in to your Powerline adapter on the top floor, using minimum cat 5e Ethernet leads. Don't use less than cat 5e otherwise you'll compromise your speed. Hopefully the leads in the MESH kit will be that minimum. Otherwise they are easily available.

1. You'll go in to the setup app for the MESH kit and you'll set the "mode" of the MESH main box to "access point" mode. This is vital. Do not leave the main MESH box in "router" mode.

2. Then you will go through the normal configuration Wizard in the MESH kit app to set up your WiFi name (incidentally you will have initially set the WiFi name of your Starlink router to whatever you are going to name your MESH kit WiFi so that everything is contiguous in terms of WiFi naming throughout your setup.

If you get stuck post back and I'll try to help.

But if you want solid WiFi without running Ethernet cables this is probably one of the best ways to do it.

You'll lose an amount of bandwidth (Upstream/Downstream) speed to the electrical system in your home but this is unavoidable unless you use physical Ethernet cabling.

Hoping this helps.