But I am still waiting for my pro minis to arrive and only have a old one with a ATmega168. I read something about disabling the debug in mysensors.h. Will I still be able to fit an button sketch with wireless using the smaller ATmega168?

Cheers
Al

@Chester Cheap and good looking would suffice. because these switches wouldn't switch any real current, safety shouldn't be a problem.

What about NRF24LE1 NRF24L01+ MCU Wireless Transceiver Wireless Communication Module NEW

Would that work as a battery powered wireless switch? can I just upload any mysensors sketch to it or is it to limited for this?

I will be using the 5031NMS, which is the slave button, so it has a very shallow depth, fits the normal faceplates and has lit buttons that run on 5v.

So not really cheap ($20 AUD per button), but worth it for my install. The HLK power supplies, an arduino nano and RFM69 module should fit in the wall box behind these switches.

And how about the time from waking it up from deep sleep until it sends the REST command, would that take several seconds

Yes it will. wi-fi is not the best for home automation , truly speaking. If the bulbs you are controlling only listen to wi-fi, you will have to run a extra wire into the wall-switchbox , and keep and wi-fi node always running (and connected) there.

What about using only a ESP8266 esp-01 only + battery.
it has two gpio ports. I know that the ESP8266 draws more power than the nrf24 but if the switch is only flicked <10 times a day and it sleeps the rest of the time would it not be possible to run a long time on like a CR2450 battery for a decent time?

And how about the time from waking it up from deep sleep until it sends the REST command, would that take several seconds as I guess it has to connect to the router every time it wakes up. I would want as little delay as possible from pressing the switch until the light bulbs react.

they have some models with RF and there is a arduino library to control them with RF:
http://forum.arduino.cc/index.php?topic=153525.0

or you can try and make your own touch panel with cheap touch sensors inside...

You can buy the swith buttons to go into a normal faceplate, but each button will cost more than the microcontroller and radio... It comes down to the question of cheap, good looking or good quality. You can pick any two of those :)

So you could possibly look at using a battery powered version since you should be able to put a large pack of batteries in your now vacant wallswitch boxes.

Have you seen this:
http://www.mysensors.org/build/scene_controller

Even if you don't use the beautiful screen, you can use some of the code.

The part you left out is powering it, which could cost more than the uC, nRF and switches - or not.

Cheap power. There are some very cheap and small 5v USB "phone charger" plugs (eBay, AliExpress, dollar stores), which could be reduced to 3.3v (needed by the nRF) by the regulator on a 3.3v APM. The couple I've opened up could have their PCB removed from the AC plug tines and housing without much trouble.

Power Quality The cheapest ones may put out noisy 5V - intended for recharging batteries at best. Be sure to check the voltage. The regulator on the APM might be enough, or you might need more caps to smooth it.

Safety And some of the cheap ones have poor isolation between the AC mains and the 5VDC output. You can search for some of the investigations thereof on the web. The worst case would be mains and DC traces too close to each other, or a poorly insulated transformer.

If the buttons will isolate a user from any potential shock, and you disconnect the power before working on them, and you choose a phone charger which is not too bad, you might make a switch node for $3-4. But don't hold any of us responsible for your safety!

AND - you may have cheap power already figured out.