If you want to steal recipes and plans with less risk, use the following set up. Note, the Khajiit part is really only needed if you want to basically be invisible and undetected. I have run just one of these armor sets on my Medium Armor NB and I rarely get a detected icon. Nightshade is cheap and easy to find, you can craft night silence if you know 2 traits.

Nightshade Set: 3 piece bonus: Decrease Detection radius by 2 meters, decrease sneak cost by 24%
Nightsilence Set: 5 piece bonus: Ignore Movement Speed penalty while Stealthing
Medium Armor Passive ( 7pieces) : Improved Sneak- reduce cost of sneaking by 49% & reduce detection area by 35%
Khajit Racial passive: Stealthy (3/3): Reduce detection radius by 3 meters.

So this should equal:

Detection radius reduction of 2 meters + 3 meters + 35%
No Stealth movement penalty
Stealth cost reduction of 73%

Source:

https://forums.elderscrollsonline.com/en/discussion/292036/stealth-detection-radius-stacking

Anyway, follow at least the first 3 of the 4 above and you won't be caught unless you steal right in front of an NPC while they are facing you and focused on you (talking to you)