How can I do this with Paypal?

I'm looking for a way to do something with my website.

I had a way for someone to click a button on my website, go to pay me at
paypal, and then paypal returned them to a "Thank You" page, with a link to
the product.

Now, I have several products, and I cannot list them all on the single
"Thank You" page, because people will poach the other products through the
links.

I am imagining that there is a way for someone to be directed back to a
"Thank You" page by paypal, and when they click on the appropriate link, the
window disappears, and takes them to the download link for that product
ONLY. When the initial "Thank You" page disappears, so does any record of
it in the purchaser's history files.

Do you have a way to accomplish this, or even maybe a better, more secure
way? I do not want to pay for a monthly service or exhorbitant fees.

Please let me know,

Thanks