using the ikea LACK side table on top of my normal desk, which puts my keyboard and mouse right and hand-height. You can use a circular saw to cut the legs off to your exact specifications.
+ tall VIVO desk mount monitor stand, which raises the monitor & laptop to eye height.
+ hog heaven floor mat to stand on.
The rare times I need to sit, I just unplug my laptop and take it over to a chair. In theory, the monitor height is easily adjustable via a fast-latch, and the ikea stand can be removed, so within a minute I could be back to a normal desk - but i find the change of environment from disconnecting and moving to a separate space is more relaxing.
My lower back used to hurt CONSTANTLY, but since I've been standing it has been a night-and-day improvement. I can't recommend it enough. the transition period was surprisingly easy. I suggest taking your chair away completely for the first week or two - if it's nearby you will be tempted to cheat, and far more likely to give up, I think.