BJT vs MOSFET for very low power flyback converter
I have recently finished a similar design. We are now at the pre-production phase, having already validated the first prototypes, which operate perfectly under similar constraints as the ones you describe in your question. Because of IPR limitations, I can only give you some general guidelines.

Based on the following assumptions:


You are trying to avoid the use of a transformer by all means (which may not be the case),
The power requirements of the load is in the miliwatt range,
You don't want to step-up the voltage supply first, but will use the 2VDC directly for powering your flyback design block.
You need to keep the cost and PCB space to the absolute minimum.


I suggest the following approach:


Rule out the MOSFET and use a fast switching high voltage BJT (rated at least to 200V, better yet to 300V).
Select the most appropriate inductor for your constraints and depending on your requirements for maximum power delivered to the load.
Calculate the maximum flyback voltage, and make sure you can get at more than 200V voltage flyback "peaks". The involved parameters here are: ILpk (inductor peak current), Cts (total sum of parasitic capacitances at the flyback node) and SWITCHING SPEED of the BJT.
The last one is hugely important, and rarely mentioned in the technical literature. You may have a big ILpk and very little Cts, but if your switching (off) speed is not fast enough, the flyback voltage will suffer. Reminder: Vflyback = -L * dI/dt.


The above can be implemented with:


A simple (single) inductor or
A 1:1 coupled inductor.


Apparently, from the design equations point of view, there seems to be no need for the 1:1 coupled inductor, as the single inductor will work exactly as well, most probably with less resonance apparatus. However, using a 1:1 coupled inductor will help avoiding EMI generation. I suggest the use the 1:1 coupled inductor in case you have to EMI certify your final product.

** However the previous assumptions, should you want to explore the flyback transformer approach, there now exist very nice miniature (micro-power) SMD flyback transformers. **

For instance, this Coilcraft model allows up to 1:100 turns ratio with 300Vrms isolation among primary and secondary coils:

http://www.coilcraft.com/lpr6235.cfm