Sorry to hear what had happened to you.
I used to deal with tourists from mainland China when I was working in a theme park.
Same situation that some tourists from mainland China squat on the toilet seat and leave shoes prints and feces all over the place (I often encountered parents who let their kids to pee or to go no.2 in public area as well), I think it has something to do with the cultural preference since many of the toilets in mainland China are squatting design. You may wanna do more research about if this habit is specific to China or in some other countries as well.
You may look into some references from countries that take lots of tourists from mainland China like Japan, there are public facilities such as the airport, provide squatting toilet or signs that are written in both English and Chinese to let the tourist know not to squat on the toilet seat for others' consideration. I wouldn't think to put up a sign specific to certain people with certain habit as a discrimination or an offended act. It would actually be a good thing to do so to let the others respect your/particular culture.
In your case, it doesn't seem necessary to make a squatting toilet just for occasional tourists with squatting preference.
If I am you, I would put a sign on the restroom door in the language which you host most, to ask the guest to please respect your place and the others, at least to clean up if they do so because you are hosting a place for vacation but not a commercial hotel. Also, go with a penalty notice if anyone made such mess, as I would see it as property damage for leaving any area dirty and unhygienic.
Hope it helps.