How do I extend my WiFi while using the same SSID?

Hi all, I want to share a printer (Epson ET-3600) throughout my home wirelessly and I am unsure and confused as how to do this. I have a Comcast cable modem/wireless router in my basement which gives WiFi that works fine for my basement and first floor, but not my second floor. I then bought and installed a D-Link DIR-810L wireless router and installed that on my first floor. The D-Link does provide good wireless coverage on the second floor but I had to create a new second WiFi network using this device. Now I have 2 WiFi networks in my house. Let’s call them Main and Second. I was told I should get a device to replace the D-Link WiFi router that would be able to boost my WiFi on the second floor but keep the same SSID that my Comcast modem/router provides, the one named Main. Once I do that, then I can share my printer on the Main network all throughout the house. Can somebody please tell me what extender device to use and how to accomplish this?  Thank you very much. Marc