As first approach the architecture is the following:

Wifi & Controller.

Cheap Wifi modules are available but most popular are ESP8266, ESP32 due to huge user base and friendly development environments such Arduino IDE.  Other alternatives such RTL8710 could be considered as experimental for makers, Also for battery powered application ESP show better results (https://blog.voneicken.com/2018/lp-wifi-other/)

ESP32 would be the best solution as it:

1. Super fast dual core.
2. Has Wifi & BT.
3. Has lots of IO pins with several ADC entries.
4. Has a ULP processor that can use TWI and analog inputs & RTC to wake the main processors. UPL could act as a simple controller.

But for the project it present some issues:

1. Too much features for this simple project.
2. Bigger footprint.
3. More expensive then ESP8266+controller.
4. ADC accuracy is on dispute for this chip.
5. UPL require asm programing which is not friendly.
6. Higher power requirements in run mode: Recommended regulated power to 500mA for peaks.

My decision  was to experiment with STM32 family for the controllers. In particular with the cheap STMF030F4 that can be adquired for less than $0.5 in small quantities.

Radio interface:

Standalone radio modules with SPI interface.

LORA

For Lora Hope RFM9x are very popular and are widely available for $5-$6. This modules have improved alternatives with shielding and FCC certification such HPD13 and NiceRF Lora1276-C1.  They share same pinout and are interchangeable. Reference https://www.rocketscream.com/blog/2017/08/21/the-sx1276-modules-shootout-hoperfs-rfm95w-vs-nicerfs-lora1276-c1-vs-hpdteks-hpd13/

Key parameters:

• 1.9 -> 3.6 V input voltage typical 3.3V
• SPI interface up to 10Mhz wih additional 3 IRQ lines (high level).
• About 120mA peak current during Tx.
• Typical freqs are 868Mhz(Europe) , 915Mhz (USA) , 433Mhz (China).

NRF24

Improved SMD modules with cloned nrf24L01+ with chipset Si24R1. This claim to be compatible to and have with enhanced output power. AI-thinker's NF-03 module https://datasheet.lcsc.com/szlcsc/Ai-Thinker-NF-03_C115101.pdf is available for $2-$1.

Key parameters:

• 1.9 -> 3.6V input voltage. typ 3.3V
• SPI interface with 1 IRQ(optional) low level up to 10Mhz.
• About 15-20mA Tx peak output.
• This module uses 2.4GHz ISM band.

RFM69

FSK modem RFM69 are also used in DYI project as they. The radio footprint is compatible with RFM9x only in the  HCW versions. They are widely available for around $3-$4. 

Key parameters:

• 1.8 V -> 3.6V input voltage typ 3.3C
• SPI interface with 1IRQ line high level.
• About 130mA peak current during Tx.
• Special feature such hardware CRC & AES-128 encryption.
• Frequencies:  868 , 915 and 433 Mhz.

Note: As i do not use this modules software supporting this module, but a library for implementing it is available: https://github.com/LowPowerLab/RFM69

OOK/ASK 433Mhz:

There are a several transmitters of transmitters that require only 3 pin connection VCC-DATA-GND. With standard 0.1 inch headers. Some examples are shown here: https://goughlui.com/2016/05/01/shootout-four-433-92mhz-askook-transmitter-modules-compared/

They are really cheap. Some stores offer 5 pieces from less than dollar.

Power Management:

Must provide the device with stable and regulated output that support with ESP and controller.

Temperature Sensor: