Hi WWW, Sounds like what you need to do is:
Click mumsnet classic. This resets you to unlimited messages per page, and most recent first order. Then, on that same page, On that same page, flip the order selector box to "book style" and click save at the bottom of the page.
Then you'll have old mn, except that the op will be at the top of the page and the thread will read down the page, but all messages on one page. Is this what you are after?