There are a number of tools available for viewing 35mm trannies. A 50mm lens turned around works very well. Over the years I have accumulated quite a variety of loupes and magnifiers, but if you are looking for one specific for 35mm film it should have a transparent standoff that is sized to fit directly over a 35mm frame. These were once common, nowadays probably not so much.
I find looking at them with both eyes is much easier on both the eyes and the brain. In the 50's and 60's Pana-vue made a Bi-lens viewer that used half silvered mirrors to split the image for each eye. A good binocular loupe can also work well.