There is stable in-place merge sort, it runs in O(n*log(n)^2). It is about 3 times more complex than shell sort. I implemented it here https://github.com/thomasmueller/bau-lang/blob/main/src/test... (most sort algos you mentioned above are in the same direcory btw)

You didn't mention heap sort. A simple implementation, which doesn't do any method calls just like shell sort (also next to the merge sort above) is about twice as complex than shell sort.