I think you are doing things well. We have a person in the group that still brews on the stovetop. Hand scoops the grain into the mash pot and also transfers the mash wort to the boil kettle by hand. He only uses 35ppm. So If I were in your position, I would use 50ppm of sulfites and try to be careful. Check the condition of your pre-boil hot break foam as to how white/consistent and free of tieg it is. That is really the best indicator of how the mash went from a low oxygen perspective.
Lowering the bag is not a big issue, it is raising the bag out where all of the oxygen comes into play. The next best hardware change is having a separate boil kettle to drain away into rather than a single pot. But, you have to use what you have and brew the way you brew knowing you might not get all the way there but judge if you see enough improvements. It is not easy to minimize most of the O2 intake without the help of the right setup.
What about raising the temp of the mash almost up to boiling before raising the grain out? Sort of like a very hot mashout? As temperature increases, less oxygen is retained in the liquid. That might mitigate some of the damage. If you have a pulley system maybe raise the mash up to 185F and start your slow raise a bit at time to let a lot of the draining happen below the water line (most important part). So by the time you have the bag out, a) there is little to drain & splash and b) you are close to boiling so the wort will not hold on to much oxygen anyway. Keep your pH at normal mash amounts (5.4-5.6) and you should not have any tannin issues.
Just a thought. Either way, slow, slow, slow with the bag is your best bet.
I stir the mash once after all of the strike water is in the mash tun. I run a recirc the entire mash with a slowed down pump using a PWM voltage controller. This allows me to control the speed of the wort flow by slowing the pump impeller instead of having it spin at full speed and beat up the wort. During chilling I have a motorized stirrer going at 35RPM the entire time. So you can do things to the wort, it just needs to be slow and gentle.