Improved premotor filter
I just tried to install a Hoover S bag on my Dimension 1000 after reading above and it will not work. The bag will hang loose at bottom and bag door won't close. Also you'd be barely filling the design of that bag compartment with an S because of the new bag angle.
I do not know of any generic Hoover M bags that would work better than the Hoover. However, I have heard of collectors taking the Hoover M bag collar and gluing that cardboard to a Kenmore HEPA cloth Q canister bag. I have not tried this myself yet though but plan to at one of my next bag changes. The Kenmore HEPA cloth bag is gigantic so it will leave you with enough room for bag to fill which is a completely different story if you were to use a HEPA S bag.
Another option which I have done and recommend is improving the premotor filter. The genuine Hoover Dimension filter is very thin. You can substitute that with HEPA cloth bag material cut to fit or also Muslim cloth. I was recommended by another collector to use 4 layers and try the Muslim cloth and I've been impressed. Go to Joann fabrics and it's a thin white, non see through cloth. It's very cheap but works well. Just take your filter compartment door and cut the width and then fold cloth down to get 4 layers thick which is still thin enough to put in the filter compartment. Upon checking filter cloth after many uses the front cloth is dirty, the back cloth is white!!!
I have 2 Hoover Dimension 1000 canister vacs. I've had the Muslim cloth 4 layer filter system in use for both machines for about the past 6 months and have been very pleased. I use genuine green Hoover M bags with scent tablets.
My Hoover PowerMax and Windtunnel canister have Hoover S HEPA bags installed with genuine Hoover normal pre and post motor filters.