There are two ways I can think of: ctrl–E and ctrl–Y scroll the buffer without moving the cursor’s position relative to the window. I think that is what you want. Also, if you set scrolloff to a large number, you will get the same effect as ctrl–E and ctrl–Y with the movement keys. scrolloff setting will make it hard to get the cursor to move vertically relative to the window though. (Use something like :set so=999, so is an abbreviation for scrolloff.)
:help 'scrolloff'
:help scrolling