Paused RDL's/Deadlifts would probably be more beneficial for your deadlift than trap bar.
Film your bench form, chances are you might have your elbows out to wide and bar too high on your chest. (no lats). Pin Press/Board Press/Floor Press should all help your bench![]()
I don't have anyone to hold a board

To be honest I think I can progress without these at the mo, just by fixing my technique like you say. I was working on that today and did feel stronger for it.