Yesterday, we just did a TPLO on a SIXTEEN year old border collie.Today, Fly is fully weight bearing.
I have yet to see a TPLO done by a good surgeon result in a longer recovery than conservative management.
Id say 90% of our dogs that get TPLO’s (and we do on average 6-9 per week), are fully weight bearing by day 3, and back to restricted leash walks by day 5.
We never recommend crating (unless dog is used to it). We always recommend avoiding stairs and slippery floors.
I wouldnt be concerned on how your dog would handle it, its a much faster recovery than conservative treatment - same with a tightrope, TTA and lateral suture. However, finding a good surgeon is the most important part!
Here is a great summary: http://www.ovra.com/home/ovr/page_179/cranial_cruciate_injury_in_the_dog.html
Sounds like your dog would likely do just fine with a lateral suture as compared to a TPLO. I say this because you say he is calm, and is lean bodyweight.
I personally would opt for the surgery - the conservative treatment is going to keep him JUST as confined as post surgery, and the recovery with surgery should be much faster.