Need to replace a door sill/threshold

Our house was originally built in 1908. The cement steps in front that you see the top of, do not have your typical landing, since this was originally built as an open porch, and what you see was a step to the landing in front of the main door. In the 30's it became an enclosed porch, so the sill/threshold now acts as one more step without any landing in front of it. It is exposed to New England weather. One end is now beginning to rot and come loose. The original storm door was finally replaced in 2000 to an aluminum storm door, but instead of opening outward as you would expect, we could not do that by code (no landing), so the storm door was installed on the inside of the frame and opens inward. You will notice in the photo, the sill/threshold does not extend under the storm door frame. This causes all the rain and snow to seep under the door, since the door only hits the back side of the board. We are now starting to have trouble with the porch flooring.
The sill/threshold that is there now is shown below. It's a 2" x 8" (1 1/2" x 7 1/4" nominal) Oak Sill Nose Molding:
https://www.homedepot.com/p/Alexandr...0...
Unfortunately, the board is actually too narrow, and the door stops at the rear 1/2". In order to correctly fit a threshold, so the door rests on the high section as it should, it needs to be 8 1/2" (actual) width i.e. find a 2x10 board.

I need to replace the current sill/threshold with a wider board that will fit under the installed storm door and frame. I need to replace the wood that is there (7 1/4" wide) with a board 8 1/2" wide. That will allow the storm door to close on the top of the threshold. Originally I wanted oak, but it is only available as special order, even at hardwood suppliers. I've purchased 8/4x10 soft maple from them, but I'm not sure it would hold up.

I need to use something that will take the abuse of being stepped on, on a daily basis.

I'm hoping someone can give me some ideas.

Thanks