@Joguirian 

I may be able to help you with that, but I will need you provide more information so that I can give you good options.

In general, to have good coverage you will need at least one WiFi mesh unit per floor. Might be more, depending on type of house, WiFi interference and so on.

Here is first set of questions I have for you:

1. What is the speed of your Internet connection?

2. What is your router brand name and model (so that I can check its specs and capabilities on the Internet)?

3. Do you have good WiFi coverage everywhere on the 2nd floor, where your router is?

4. Is you router placed in the middle of the 2nd floor or closer to the side of the floor?

5. Main WiFi mesh node will be side by side with your router. Can you place other WiFi nodes on other floors exactly above and below router and main WiFi node? You will need electrical outlets for that available at these locations.

6. Any chance you have Ethernet cable(s) going from the router to other floors of your house?