Matilda - "I think certain things shouldn't be for sale. who here on this thread thinks slavery is OK?"
Slavery is not OK because the slave receives no renumeration for his labour and does it because he will otherwise be beaten/killed.
People who are paid for their menial labour exist everywhere today. Cleaning ladies, farmers, etc do what slaves used to do. The only difference is that they are paid for their labour.
"Bodily things and labour can make people ill, and keep them under the control of others legally and through poverty."
Like mining, for example? It is very physical labour that puts the worker in danger on a daily basis and in the long term. It is paid labour and it is legal.
"So my perspective on this, as with prostitution, isn't from the point of view of what restrictions we should place on what people do with their own bodies"
But that is the consequences, regardless of the POV you feel you come from. You want to restrict people from doing something with their body that they want to do, which does not necessarily harm them.
"it's from the point of view of what sort of society do we live in where powerful people feel it is defensible to use the insides of very bodies of others"
Why is it OK to use the outsides of others' bodies (the hands of a masseuse, for example) but not the insides?
"I'd place altruistic surrogacy for a sister or close friend in the same category as mutually consensual enjoyable sex... Paid surrogacy goes with prostitution, paid organ donation"
Unfortunately for that argument, many women do choose to be prostitutes (often temporarily) out of their own free will and it is mutually consensual. I have heard some say that it is even enjoyable and thrilling.
There are many surrogates who say they enjoy being pregnant and being able to help couples desperate for a baby. It is of course consensual, as well.
From where I am sitting, this is looking like you wanting to impose your morality and your understanding of these issues (sex for money cannot possibly be mutually consensual and enjoyable?) on others.