John Alsop was an airline pilot and he designed the Triton 24. The Mystere is basically the same hull with a clipper bow and raised stern for more interior room. The rudder shifted to the transom. I think The Mystere was meant to be a bit more upmarket than the Triton which continued for awhile. I personally think for the same money you could do better with a larger boat. I would also try and avoid any boat with an Yanmar YSE8! Some people like them but you will be budgeting to change it sooner or later.

Welcome to the forum.

Keep an eye out for yachts at Batemans Bay. I would suggest concentrating on yachts 26 to 30 feet. You really need standing headroom and an inboard diesel.
There are heaps of boats about that suit and in that price range. Here is a local boat, I don't know it and it has a diesel to be avoided but its an example only
http://yachthub.com/list/yachts-for-sale/used/sail-monohulls/columbia-27-sloop/177375

This is my pick. May as well start at the top.

www.gumtree.com.au/s-ad/bli-bli/sail-boats/s-s-yacht-maring/1097153416