In hospital

I can't say much about the actual operation because I was (thankfully) completely unconscious, but I later learned that it took about 5 hours and involved the removal of about 400g of tissue from my right breast and 500g from my left breast.
I found this animated video to be very helpful in preparing me for the operation, and this simple diagram of the procedure is also worth studying.

The anaesthetist arranged for a PCA pump (patient-controlled analgesia), so I could just press a button if I was in pain and the pump would deliver a measured dose of intravenous pain control. In fact I only used this a couple of times and at no time was my "pain score" any higher than 5.

The morning after my surgery, the first thing the surgeon checked was my nipples. Because the procedure involves cutting all the way around them and lifting them to a new position higher up the breast, there is a risk that the blood and nerve supply will be damaged, leading to loss of sensation or even “death” of the nipple due to lack of blood. This is one of the most serious complications of a breast reduction, and patients are always warned very clearly that there is a (hopefully very slight) chance of losing one or both nipples.
Fortunately mine were still pink and perky, so that was one hurdle passed.

While in hospital I had a tube in each breast, draining blood and fluid that collected after the surgery, and I was on intravenous antibiotics for 3 days as well. So although I could get up and walk around without too much discomfort, I had bottles and tubes to manage as well.
On day 3 I was allowed to have a shower, which was blissful, but unfortunately the nurses were a little over-enthusiastic in removing some of my dressings, and took off a large piece of skin on the side of one breast. This was to give me more trouble than the actual wound, because it was initially very painful then intensely itchy, and remained so for several weeks as it gradually healed.
To my great relief and astonishment, the wound itself was almost pain-free, mainly because the bottom half of both breasts was completely numb due to nerve damage. This is very common, and usually sensation returns over several months. But with wounds totalling over 20 inches in length, the numbness is a blessing, and by the 3rd day I was taking only simple paracetamol, without needing codeine or anything stronger except when the drains were removed or the dressings changed.