How do I deal with and purify myself from urine spray that splatters on me when I relieve myself on the toilet, and how do I wash it off, given that I spend a long time purifying myself, which has caused me psychological and physical distress?

It is clear that you are afflicted with waswasah (obsessive whispering), and its cure is to ignore it and turn away from it. If you are not certain that urine spray has reached your body, then nothing is required of you, because the default is that no impurity has affected it. However, if you are certain that it has affected a specific spot, then only the affected spot needs to be purified by pouring water over it. Washing the entire body is considered blameworthy extremism (tanattu'). As for the bathroom floor and wall, if you are certain they have been affected by impurity, it is sufficient to pour water over the affected spot. If the matter is doubtful, then ignore the waswasah.