Poor Monty and poor you. As you may know if you have been through a big surgery with another dog, the first days are the hardest - the surgery site is so new, and you and he need to get into a routine and smooth ways of doing and handling. If you live alone, see if someone can come and stay with you for at least the first day or two, if only to keep an eye on Monty while you have a break or run an errand.
Here are some other things that helped us when Rickie had his surgery for hemangiopericytoma - he must have had a 100 staples - they had to create a skin flap because of the amount if tissue removed.
- you can get people incontinence pads at the drugstore that are plastic on one side and absorbent on the other, if that helps with the bedding instead of / in addition to the plastic underlayer on the bedding
- we confined him to one room (the kitchen) where there was no furniture to climb on, and where he could be in a safe corner but still where the action is
- my husband or I was with him continuously for the first 2 weeks - we are fortunate in having jobs that allow us to work at home when we need to
- we were religious about putting a cone on him except when we took him out to potty (like you, leash only in the backyard for the first while); tried the bite not and the soft cone but found the rigid one worked best - YMMV - he had no spare tissue so it was crucial that he not tear open the incision
- we got one of those soft compresses from the drugstore that you can heat or chill and we used it, wrapped in a dish towel, alternating warm and cold, several times per day - the cold for swelling, the warm to encourage circulation (may not be an issue for you - it was for us because of the flap needing to maintain blood supply - we didn't want to lose any skin). Check with your vet if you like this idea, because with the drains etc., it may be contraindicated in Monty's case.
- we turned the dining room into a bedroom - pushed the table and chairs into the living room and closed it off, then moved a mattress to the dining room, along with multiple dog beds (again, nothing to climb on)
It does help in the early days that the pups are on so much pain medicine that they don't want to do too much anyway. I hope things go smoothly. You and Monty will be in my thoughts and prayers.