Choosing the Right Engine for LPG Installation in Mazda 3, Toyota Auris, or Mercedes B-Class

Hello
I am faced with the choice of buying a small car for my wife, who, however, does a lot of kilometers and for this reason I would like to install a gas installation. The price of the car is about PLN 40,000 - 50,000. The cars that I (my wife) are interested in are: Toyota Auris / Mazda 3. I also looked for the BMW 1 Series, but it has some poor opinions, so I guess I'll give it up. What else do you think about the Mercedes B class? Anyway, everything I look at doesn't like gas. At least that's what I find on the internet. Please advise what engines to look for in these cars so that there is no problem with the gas installation. I am interested in low mileage, and thus relatively young cars with newer engines (which do not like gas) .
If it is impossible / does not make sense to install an installation in these cars due to high costs, what cars do you recommend in this class?

Make sure there is an indirect injection, I do not recommend Japanese, maybe some KIA.

Merc B runs on gas. For this money it is practically a new Grand Punto, excellent with LPG. I already beat 3 years Jazz 3 100KM with LPG. Irreproachable. 7/100 with air conditioning.

That's a billion opinions. It all depends on the gas generator and you. If he can and wants to do it and you don't regret the money, then everything is up to you.

Thanks for the opinion. I take auris 1.6 from 2016. Gazownik claims that BRC will be fine. At my request, he will also add lubrication.