Bad choice. Your application likely needs 2 serial ports (bluetooth and sensor), the tiny84 has none, and more than one software serial port is inadvisable.
The 841 might be what you want, assuming you write your code tightly enough to fit in 8k... it's a pin compatible part, but has better peripherals (2 serial ports, another 16-bit timer, more adc pins) (but isn't available in the throughhole package)