Pulse oximetry
Pulse oximeter
Here is some information on both basic oximetry and a list of OSCAR-compatible oximeters.
In regards to tidal volume. I have been diagnosed with hypoventilation by failing a couple of room air overnight Cap/Ox tests. I have had lots of interactions with my Pulmonologist and RT regarding this.
Tidal volume usually decreases as respiratory rate increases. And vice versa. Minute ventilation is the key here (MV = VT + RR).
1. Increasing EPAP can help by stenting the airway more (so larger volumes of air coming in).
2. Either Pressure support, EPR, or a or c flex like you have (or softPaP for Lowensteins) can give a little extra boost to the inhale, increasing it.
3. There are machines with back up rates (ASV for normal person with CA's; and ST (A) or equivalent for someone with lung issues, etc. - like COPD, or Neurological implications).
4. The last category is ventilators. These ensure an "x" number tidal volume with every single breath during the night (and can even be used during the day).
Your situation doesn't seem dire to me at all. Hopefully, with some tweaks, your tidal volume can increase. If not, there are plenty of different machine to advance to.