OP, then I learned how to double lunge it was on a horse that had been there, done it all his life. Teaching a new horse can be confusing, for both horse and person. I know you said not to tell you that you need someone experienced around, but I'm going to say it. Only because it's really hard to describe what to do over the Internet, and in the moment you may have to make small adjustments where an instructor on site can come in super handy.
YouTube vids will be very helpful. If you feel ready to go for it, how about try it out at the walk only (for your safety and horse's), then come back and ask a more specific question about obstacles you encountered while working.
I've read a little about it, I'll post some information and you can make your judgement :)
There's a nice article that sums the double lunge nicely.
"Introducing a horse to the double-lunge
When you first start, make sure you are in an enclosed space, which could be a round-pen or an arena. For safety reasons no other horses should be around. Of course it always helps if you have someone who already has experience with double-lunging. For example I like to have newcomers work with one of my experienced horses while I simultaneously teach that person’s horse the principles of double-lungeing before they take over. That way we can avoid the famous “green trainer/green horse” experience J
Some people prefer to double-lunge in a halter or with a caveson, but I like to start my horses with a regular snaffle bit. Of course the horse must be familiar with a bridle, which I typically introduce in short sessions over the course of several weeks. Additionally I introduce them first to the single lunge, so they have a concept of going around the handler. This might be done in a halter, to avoid pulling on their mouth. Only when they have mastered single lungeing do I introduce the double-lines.
I begin teaching my horses in a surcingle which they should be introduced to while single lungeing. If you are using a saddle (because you will be riding or to familiarize the horse with the equipment), then you must take down the stirrups and connect them underneath the belly of the horse (we often use old stirrup straps to do the job). The double-lines will then run through the stirrups instead of the surcingle rings.
It is very important that the double-lines are made out of one piece, with a snap each at the respective end. Having two unconnected, single lines is much harder to handle and reduces the ease of turning the horses. My lines are between 40 and 50 feet. Shorter lines are easier to handle, but require smaller circles (or a lot of walking of the handler!).
If your horse has never had a blanket put on and is not used to anything touching him, you should gently introduce him to the feeling of having a lunge line behind their hind legs. Depending on your horse’s age and temperament, this might be all you can accomplish in the first lesson. If your horse is quiet and relaxed, then you can start with attaching the double-lunge to the bridle (or if you prefer it can be a caveson or halter).
Stand on the left side of the horse and bring one end of the double-lunge through the stirrups or lowest surcingle ring and snap it into the left bridle ring. Praise the horse. Make sure the horse stands still until you have put the double-lunge on both sides. It may help to have a person hold the horse while you hook up all the necessary equipment, especially if it is your first time.
Put the other end of the double-lunge over the saddle to the other side. Again bring it through the stirrup and connect it to the right bridle ring. Go back to the left side of the horse and ask them to go forward once you have organized the double-lunge and whip in your hands. Initially I “drive” my horses and walk behind them (at a safe distance) and allow them to get used to the equipment in a calm and steady walk."
There's also this equipment:
Horse Double Lunging Draw Reins,Double lunging and driving reins. Combined with the web rein and the rope to ensure the reins pass through the rings easily. Can be opened in the middle.