You'll find a lot of information on decimation filter design in the yellow book by Prof. Temes.
One point I'm not sure to understand.... You said the LPF output must be 1 bit. Is it your design requirement?
Honneslty if that's the case it's difficult. Indeed decimation filters reduce the frequency but increase the number of bit to keep the resolution.
Here are some ideas:
- Decimation Filter + Digital DSM -> you can put back to 1bit resolution but need a little OSR. Maybe less than the initial one.
- 1bit LPF: I've seen some article recently in a conf. (sorry I don't have it) about 1bit digital signal processing
Good luck