I made one similar to the one that you have shown.
Used plywood, and screwed it onto the ironing board.
Stapled flannelette in layers til I had what I wanted for padding.
Then made a couple of removable covers.
Take one off, and put the clean one on at the same time.
As mentioned ... you need to watch sizing of the board to the original framework.
Too large, and you will lose stability.
Also, too much overhang, and it will not be stable.
A lot depends on how heavy duty (or flimsy) the original ironing board is.
And bonus .... when entertaining, I put a tablecloth on the ironing board, and have an extra serving table!!