I have a problem in that I have no way of practicing the initial decision making - has anyone got any advice on that?
What an excellent observation, and question!
This is a woefully overlooked element in pilot decision making training. It's the "fight or flee" decision making process, flight to continue to fly it, or flee to the ground, essentially giving up the flight to keep flying. The possible availability of a BRS adds a whole other element to that, however, the scope of this discussion is an emergency at a low enough that a BRS would not be of much use anyway.
I have had a total of six engine failures/major power losses during my flying, with three being EFATO. In all cases, I was able to land the aircraft ahead, in a place from which a later takeoff was possible - lucky me! But the "fly the plane" element remains vital in any case. A mentor of mine once told me: "point the plane at a place you think you could crash, then don't crash when you get there.".
The decision making as to "just land it ahead", or cause check and search for a good spot, will be based largely on the length of time available to you to glide to your short final approach, and arrive there with suitable speed for a power off flare and landing. In most power planes, and EFATO at less than 500 feet means that the time to do anything before committing to a landing ahead will be near zero - push the nose down, and land it.
In my considered opinion, pilot training and mentoring spends too much time teaching cause checks, looking for a good spot, and flying something like a circuit around it, without actually landing on it. Looking for a good forced approach spot should not be something you begin to do when it all goes silent, it should be something you are always doing if you're not watching for traffic, checking your position relative to the chart, or checking that all systems are operating normally. Looking for a spot should be a part of your regular flying scan.
Cuase checks? Yeah, perhaps you have forgotten to change tanks - easy fix. Cause check things like that before the engine stops, rather than after! Do cause checks throughout your flying as a part of the aforementioned "checking that all systems are operating normally". If the engine has stopped due to something like an oil failure (pressure/pump/quantity, you're gliding. Similarly with total fuel exhaustion, or total ignition failure. Very few failures can be fixed right after they have occurred. Carb heat/alternate air would be one of the few things you could do after the fact. That said, one trick I once used during an engine failure at night was the use of the primer. I had had ice crystals in the fuel (before I learned to use alcohol), and the fuel flow was interrupted. As I glided down in darkness from 6000 fee, I ran (sort of) the engine by pumping the primer, and that ran it enough, that between carb heat, and the rapidly changing power settings, the obstruction cleared, and I was able to continue. The benefits of cruising at higher altitudes!
But, EFATO, decide to land ahead with no delay. Maybe you have time for a quick cause check, but probably not, and don't surrender any opportunity to keep flying the plane to cause check.
Practice forced landings to the surface, and to touchdown. Pilots get too little opportunity to practice being in the flare, and making the best of a less than ideal approach, a practice forced landing is a good opportunity - don't pass it up! Sure, the instructor once a year will pull the power back on you during a check ride, and you'll find a perfect field off near the horizon select some key points, and spend a lot of time head in, reviewing systems. At 150 AGL you'll get the word to go around. What a wasted opportunity! Land the plane!
Now, of course this means that practicing to a suitable runway would be a good idea - do that! Sometimes the airport is quiet, ask the tower if you can fly some practice forced approaches, with no circuit dimension restrictions - they might say yes. In July I did this twice while mentoring a fellow pilot. At both Osijek, Croatia, and Bergen Norway, the airport was quiet when we arrived. May we do some PFA's please? Yes. My we fly a non standard circuit please? Yes. I had my charge fly some PFA's from a very tight downwind, about over the tower, to a mid runway touchdown. After about ten of these, he was catching on well. It required a full side slip through 180 degrees of heading, with extending flaps on the way down to dump the altitude, but with a bit of practice, he was within a hundred feet or so of the aim point selected during the base element of the approach. Later, with that skill, we flew another dozen or so onto the ocean in a fjord (it was an amphibian).
I have only once in recent memory flown a PFA which was a planned overshoot, and that was in the Cub, as it was a farmer's field, which I did not know well, and the exercise was to position the aircraft to the flare in between some obstructions, so the landing was not the focus. Otherwise, If I state it's a PFA to my charge, it'll be to the surface.
The decision in a light single should be to put it down, unless you have thousands of feet of altitude to play with. There is too much risk of turning a "makeable" forced landing into a crash, because fiddling around distracted you away from simply flying well. But all the practicing you're going to do will show you how much of your attention can be diverted from flying during a glide to a landing - not as much as you thought!