For 12 bits resolution you will need around 75dB of SNR, assuming that your signal bandwidth is around 100Hz, you can easily achieve that SNR with an OSR of 50 with a single bit quantizer and a second order loop. The main issue is your input signal level, since it is a sensor I will assume that the input level is very small, less than 10mV so your noise floor needs to be even at lower level, this means that you will need to increase your OSR or your filter order to achieve an effective 75 dB of SNR. if your input signal is at -40dB, then you will need your quantization noise, thermal and flicker noise together to lower than -115dB, then you will need an OSR around 300 to achieve that.
I will recommend you to go through the book "Understanding Delta-sigma Data Converters", Schreier and Temes. They cover pretty much all the basic stuff to start with. Then you can come with some conclusions and tradeoffs for your filter.