Do you guys consider it cheating in a blindfold speedrun if I have items on my desk that guide my mouse hand in the correct directions/distances?

There aren't really official rules on how blindfolded runs are supposed to be done, people just use their own judgement for what makes sense. What you're suggesting sounds impractical (unless it's a fairly short or simple game, in which case, do you even need it) but if you can pull it off then I personally would not find it to be objectionable.

I might label it as TAS since I am getting physical info from outside the video game

Definitely do not agree with that logic, that's like saying looking at your keyboard during a normal speedrun is a tool assist.