Your Y2 is likely a K2 or very close. There are a lot of designations from different manufacturers for colored filters, but the Wratten numbers are the standard.

Finding a no. 12 filter is a bit more difficult, as they are less common. Furthermore, for the scene you describe, there will likely be no appreciable difference except the loss of speed due to the filter factor.

For flat scenes with no strong color differences, your best bet for increasing contrast is to increase development or print on a higher-contrast paper. Filters only work when there are color differences. Polarizers are dependent on the presence of polarized light, which is in short supply on overcast days and subjects that do not reflect like mirrors. You can always look through the filter and turn it to see the effect. If you see nothing, then neither will your film.

You can bracket a scene with a bunch of different filters to see if that helps, but I doubt it will do much. Try no filter, a yellow and then orange and red. You'll likely just lose speed due to the filter factor and not affect contrast that much.

I find that ditching the filter in such situations gives me gratifyingly more effective speed and that developing N+1 gives me even a bit more.

My recommendations: If you're shooting small/medium format and using an averaging or center-weighted meter, simply shoot away without filter and then use a higher-contrast paper when printing.

If you are shooting LF, meter the brightness range of your subject and develop accordingly. In your scenario, an increase in development time to N+1 is likely. If you're not a Zone System user like me, you may simply want to use an average meter reading and then try adding 20% to your developing time for flat subjects such as you describe.