When buying a house, there is one less bathroom, how can I increase one

I advise you not to do it, one, it's not legal, and the downstairs can sue you directly.

Second, even if no one sues you, you will always be in trouble. Since there was only one toilet, it means that there was a straight pipe leading to the septic tank, and you can't conjure another one out of thin air. If you want to connect the drain from both toilets into this one pipe, make sure to make a hole in your floor, which is the downstairs ceiling.

I can't think about it.

If you don't open a hole in the floor, you have to raise the ground, if you follow the 3% slope, plus the pipe diameter, at least 20 cm high, the general rule, the floor of the toilet should be the lowest, otherwise once blocked, the water will flood to other rooms, and unfortunately, the sewer pipe you change, the chance of blockage is very high.

So at the very least, the two bedrooms should be padded 20 cm. Does the weight of these cushions exceed the design load? It's heavy, it's good.

Third, your plan still has the problem of hitting the wall, based on the drawings you uploaded, it is likely that you are hitting the load-bearing wall, which is also a big risk.

It depends on the type of house in your own home! Can it be increased.