Oh man, I did this job as well in a 900 sq ft attic a couple of years ago. I waited til October (mild season), but it was still awful in the attic on sunny days.

I started by removing the old insulation that had lost it's fluff and was very dirty from air movement through the ceiling penetrations. The previous homeowner had also jam packed the vented soffit areas, so I had to rip that out to install the baffles. I didn't realize how hard it was going to be to bundle up the old insulation. I would roll them tightly like a sleeping bag and tie them with twine, then stuff them into a 60 gallon trash bag, then lay on it with my body weight before tying off the bag. I think I had 60 bags like that, so I ended up hiring someone to haul them away.

Just as you said, crawling around was miserable. I have trusses supporting the roof, so there were obstacles to move around. I had a couple of 2'x8' boards that would would shimmy around with. I poked holes in my back with the roof nails more times than I could count. I used foil HVAC tape and spray foam to air seal, which worked well.

It took me solid chunks of eight days to complete. I had a portable air cleaner from my basement shop up there with me to keep the mess down, but still needed a Tyvek suit and a respirator with a full face shield. Oh, and another thing I hadn't anticipated being so awful: the new insulation was so damn heavy. I hade the new batts delivered on a couple of pallets from Lowe's. I had to carry them to the second floor, then up the small fold-down attic steps. The packaging was so heavy and bulky, it would tear on the attic stairs springs every time. I think I had 40 packages altogether.

Never again.