For a project that I'm working on I need an extremely small, power efficient wireless device (could be radio, or some other interface) to network between a series of ATTiny85s and a larger Arduino. The communication range only needs to be about 1 foot, max. I'm currently using wired I2C, so it would be excellent if someone could suggest a radio or another device that can use the two digital pins previously occupied by the SCK and SDA lines on the ATTiny. I have those two, along with one extra digital pin available for use.
This device needs to be extremely small - this common NRF24L01 package is too big and its SPI interface uses too many pins.
Thanks for your help.