Have had this kit for about 2.5 years: https://www.amazon.com/gp/product/B08C4TDK5N
The batteries at the front lasts about 5 months, in the back about 3 months (more traffic, pets going in and out).
No upgrade to the solar options, you will need to buy new cameras (and possibly new base). Doorbell can be added via the app, yes. For the entry sensors, no comments, as I have not tried them.
Just upgraded a week ago to the solar 4K version of these cameras, image is better, but not as big a leap as going from 1080 to 2K, that was a huge jump in image-quality!
https://www.amazon.com/gp/product/B0B87SM8SK

The feature of getting a zoomed snap of the person on the camera on you Apple watch is cool!

Pro versions are now listed. I just saw it this morning

eufyCam 2C Pro 2-Cam Kit, Wireless Home Security System with 2K Resolution, 180-Day Battery Life, HomeKit Compatibility, IP67, Night Vision, and No Monthly Fee. https://smile.amazon.com/dp/B08C4TDK5N/ref=cm_sw_r_cp_api_i_.jvrFb5B88B6M

eufy Security, eufyCam 2 Pro Wireless Home Security Camera System, 365-Day Battery Life, HomeKit Compatibility, 2K Resolution, IP67 Weatherproof, Night Vision, 2-Cam Kit, No Monthly Fee https://smile.amazon.com/dp/B08922VDK3/ref=cm_sw_r_cp_api_i_xlvrFbBPMQMD1

Edit: didn’t see that you mentioned you live in Italy sorry