I want to simulate giving sightseeing tours around high mountains. I want to fly around FL220. 

What would a real pilot/company do?

would you:

1. fly a pressurized plane 

or

2. fly a plane that would have better views but then install an oxygen system and let pax use nose nacelles/tube? Would this be comfortable for the passengers? 

I'm thinking more of #1, yes? or do they do both?

Thanks.

Since it's about -28C at 22,000, you'd need to ensure the aircraft was not only well heated but you'd also have to ensure everyone was happy with using nose tubes, so these would be additional distractions/responsibilities for a pilot if flying solo. That kind of stuff might suit people who are into adventurous extreme sports and stuff, but it is unlikely to appeal to a more typical sightseer. So I reckon a pressurised aircraft would be a better choice, preferably a high winged twin such as an ATR-42, Dornier 328, Antonov An-140 or some such, since you'd want plenty of passengers on board to make it worth the fuel required to get up to 22,000 and able to climb up to that altitude within a reasonable time. All three of those types, being high winged, present good downward views, they all have the safety of twin engines, which is critical if you are flying over mountainous terrain, they all have decent de-icing equipment and all possess a service ceiling well above 22,000 feet.

yeah, that's what I thought. 

but I looked at K2 Aviation and it looks like they are using the DHC3 - isn't that like a pressurized turboprop beaver(dhc2)?

This link might be of interest ,

https://www.aopa.org/training-and-safety/pic-archive/pilot-and-passenger-physiology/oxygen-use-in-aviation

Scroll down to Masks an Canulas .

Cheers

Karol