So,
I moved to a house ... (it's a bit more than a house) from 1815 recently. Getting WiFi signal from one room to another is a total no go. Fortunately each room is wired with cat5e sockets to a central patch panel.
I've had Fritz!Box routers for years .. even before they were available in Ireland. Even bought some from Marx Computers, when they were around.
Now, that a lot of the providers actually are offering these routers and availability is more common, they're not that difficult to come by anymore.
Also, as of the late version 6 firmwares, mesh was introduced. With 7.01 it even became possible to share phonelines across the mesh.
So with this place, I went a bit mad last weekend. This is what my mesh page looks like:

Full size image here:
https://live.staticflickr.com/65535/49523242597_94ab8c8708_h.jpg
I used 8 Fritz!Box routers in total (3 x 7590, 1 x 7582, 2x 7530, 1 x 7490, 1 x 7560) and 2 Fritz!Repeater 3000 .. something that should be available in Ireland soon.
All routers are connected via cat5e in each room. Some rooms have analogue phones, a couple DECT phones (Fritz!Fon and some third party), 2 mobile phones using the Fritz!Fon App and finally a DECT doorbell, that rings all extensions, when somebody is at the door and acts as intercom.
There is also a Fermax intercom system in this place, that is connected to the gate. This system has a phone interface, so I'm going to try and tie that also in, so that it can be used with the phones in the house.
All routers are at current firmware (7.12/7.13/7.14). I can now literally move from one room to another without loss of connectivity.
Unfortunately only VDSL is available where I live (70M/20M) .. I had SIRO at Gbit/s speed before .. but I do have near to no loss in speed from anywhere in the house. Coverage from one router would have been impossible here.
I figured, I'd share this and if there are questions .. fire away.
Doorbell
So for the doorbell, I was looking into a cheap and cheerful solution initially. I bought this for my previous home, where there was no cat6 or phone cable from the house to the gate, so we used it there connected to a router in the front window.
For about 50 GBP you can get this:
https://www.responseelectronics.com/shop/door-bells-and-intercoms/door-intercom-systems/era-michime-wireless-dect-telephone-and-doorbellintercom-system-246b0e31/ ... can also be found on Amazon. The specific model I use is the ERA miChime CL3622B.
The doorbell works as an intercom and rings all extensions/phones. You can also integrate a door/gate opener, so you can remotely buzz people in. You can either feed it with 12V or stick some batteries in it, that last about 6 months or more (depending on use). It connects via DECT, so no wires needed there.
The DECT handset, while not being the most fancy model, has nice big buttons. Handy for elderly people. It works perfectly with the Fritz!Box .. even caller-ID works.
/M