Elect. start generator.

Inverter generator is popular and kind to electronics. Very good but expensive is honda 2200i. One of the quieter gens. About 1/2 price is Westinghouse 2500i. Also good gets better gas mileage than honda. Neither are electric start but it can be added.

For about twice the price of the honda 2200i is the honda 3000i. It is electric start and very quiet. Very dependable. That would be my choice. There are many other brands.

I dont know of any , small, (2000 watt or less) that are electric start.
For elec start generally will be 3000 watts plus, and weigh upwards of 100 lbs.
Harbor freightHarbor freight
is an example, and this is an inverter unit to provide stable power for most electronics.
If you want a cheaper option, but not an inverter model,
Amazon

But my first thought would be to check with your insurer, is there a battery back up unit available for your O2 unit, will insurance cover it?
If not, you may want to consider a battery and home charger, and then use an inverter to draw power from the battery.

If you don't expect to need power for more than a few hours, a battery system may be cheaper and easier to work with.

I would suggest looking into an inverter first.
The smallest electric start genset would be heavy.
This is about the smallest electric start.
Genset