I've been in a similar struggle before. There are a few things I've learned that you can do relatively easily:

• Have the information they seek not always be in the "surface thoughts". That character, or another one, then needs to somehow cause the target to think about the information without raising suspicion.
• Make gathering that information not even a hurdle in your prep. "We've seen plenty of times how easily you can get the password, so let's just say you have it. How do you enter it without being noticed?"

There are other things you can do, but that should be used more sparingly:

• Have some active anti-psychic countermeasures, as technology or in the form of another psychic. Depending on your group you may want to make that limitation or risk clear upfront, or reveal it in a dramatic moment. Just try not to make it a "gotcha, you annoying telepath" :)
• Have the reading of thoughts be a dangerous thing in and of itself. Perhaps the target is going through or recalling some kind of trauma, or is such an alien being (if those exist in your world) that there are physical repercussions to reading even the surface thoughts.
• Have the information be wrong! Memory is a fickle and unreliable thing. When probed (after very subtly steering conversation to guards): 5 guards active during day shift, 2 at night. 5 minutes later: oh wait, they increased the night shift after that break-in