Have used assistance at T5 and Changi. T5 can involve a long walk, so it's worthwhile to book at least the wheelchair service (I think option 2) so you don't end up exhausted by the time you get to the plane.

If you want to have any time to visit the lounge, you'll probably need to arrive at the airport at least 2.5 hours before you're due to depart, as it can take a while for assistance to arrive at check in and for B/C gates they tend to want to pick you up from the lounge an hour or so before departure.

Changi assistance was fine, if slighty understaffed, but might just have caught them at a bad time. I think there are some buggies but not sure how these are allocated, otherwise wheelchairs, which seemed difficult to push through the carpeted terminal but got there in the end

For your medical supplies, make sure you break the shipment down into packages of less than 32kg each.

Have a great trip!

Edit: The different options for mobility assistance are I think 1) help from check in to gate, 2) help from check in to seat (can walk up stairs to plane if at a stand) and 3) help from check in to seat (can't use stairs, if the plane has steps then a lift vehicle is used). When I needed to use assistance, I initially booked option 1 for all of my trips but the check in staff always overrode this and told me to take option 2, as there are various issues with being dropped off and left at the gate, e.g. if it's a bus gate, if boarding has already started and you can't pre-board etc.