Selling your body for money is not morally right, buy by making prostitution legal you could create rules and regulations in order to protect the women who have resorted to selling their bodies for money, as well as the clients from gaining unwanted diseases. This would be a win win for both parties because prostitutes would no longer have to be degraded by working out in the streets and the Johns who were ordering them would know where to go to find them.
The point of legalising prostitution is that it becomes safer. The fact is that brothels and prostitutes are not going to go away just because we ban them, and we should accept that and instead work on improving the system. Legalising it will almost certainly decrease the risk of STDs as it need no longer be done in unsafe environments without contraception and condoms. The brothels would have to conform to certain regulations (condom use would almost certainly be among them) and it means that the abuse and murder of vulnerable prostitutes working on the street would be a much smaller and more manageable problem. Many people do jobs without enjoying them, there is no reason why prostitution should be singled out as the job which is banned on such a basis. Plenty of people who sell their body liken it to a masseuse selling their hands to their customers - it just happens to be a conventionally more 'private' part of the body. Might I add that the women who work on the streets and in grotty hotels would almost certainly be far happier surrounded by other supportive people doing the same job as them in a pleasant, safe building. It seems like your reasoning is mostly in sympathy with and seemingly in the interests of the prostitutes themselves, but it actually would be entirely in their interest for it to be legalised and most of them know that. This is hardly a reason on its own but it is also true that the government could then tax it and the money could be fed back into the improvement of the sex work industry and also public services. It is an all round win-win.