Why not just remove Perception as skill? It is the 'must-have' skill of skills
First, Perception is not a 'must-have' skill. Feeling like it is is part of the problem. In my games, less than half the PCs have Perception as a skill. You are about as likely to find PCs with Athletics, Stealth, and Survival as Perception IME anyway.
Here is what I've been thinking about doing for my games. One game is pretty much RAW, and I don't know if they are really ready for house-rules yet...
- Perception is always passive (so is Insight FWIW).
- The base for passive scores is 7, not 10.
- If you make an ability to check to notice something or figure something out, it is Investigation! You are (literally) looking for clues and tells, etc. that will reveal the truth of the situation (is there a secret door over there?). You are paying attention to noises you might have heard and trying to uncover the source of those sounds. And so forth...
- You can take proficiency in either Perception, which boosts your passive score.
- Greater innate capacity in these are accomplished through the Observant feat, which already impacts Perception and now does Insight instead of Investigation (which is always active, not passive).
- Disadvantage and advantage are a -3 or +3 mod to your passive scores, not +5.
For example, if you have:
- Passive Perception of 12 (base 7 + proficiency +3 and WIS +2)
- Passive Insight of 9 (base 7 + WIS +2 only)
- Investigation +6 (proficiency +3 and INT +3)
A bad guy is sneaking up on you and rolls 11. Your passive perception 12 kicks in, alerting you to a noise or something.
BUT what made it? Where did it come from? You tell me you look around for the source, and pay greater attention to your hearing. Now, I'll tell you to make an Intelligence (Investigation) +6 check. If you roll 6 or higher, you see or hear the bad guy and know generally where they are (depending on light conditions, line of sight, etc.).
Now, if the bad guy had rolled an 18, then your passive perception failed and you won't hear or see the bad guy coming!
But, if you are "on watch" or something, you make an Intelligence (Investigation) +6 check and your roll replaces your passive perception while you are "on watch" if it is higher. If you roll lower, your passive perception is used.
Another example:
Suppose you are talking to a captive who is lying to you. I make the Charisma (Deception) roll and compare it to your Passive Insight 9.
If I roll 14 (beating your passive insight), your character believes the information. You, as the player, can always decide otherwise of course.
Now, if I roll 7, your passive insight 9 kicks in and I inform you that you (and your PC) believe the captive is lying. But depending on the information giving,
WHAT is he lying about?? Perhaps the number of enemies, their defenses, or even their location? Perhaps he is telling you something that will lead you into a trap? So, you make an Intelligence (Investigation) roll to determine just what he is deceiving you about.
NOTE: "Passive" scores are totals for something you are doing in the background, not actively attempting to do. For example, if you are watching TV, you might still hear someone unlocking a window or opening a door, but you aren't trying to hear those things... you are watching the game.
I use the term "Routine Checks" for what 5E calls "Passive Checks". Checks done repeatedly assume a base average of 10, as do times when I need a roll to be secret (if I can't just have the player roll behind the screen...).