Task Difficulty in BXDH

As editing progresses in Sorrow in Haven, I've been running a campaign with multiple parties in Castle Gargantua. I modded up Basic D&D (I'm calling the system BXDH) with a simple "Aim for 20" resolution system.

Aim for 20 in a Nutshell

• Roll 1d20 + level  + modifier. If the score is 20 or higher, you succeed.
• Level is character level, except for attacking (which is BASED on level and STR or DEX modifiers for melee and ranged).
• Modifier is an attribute modifier, saving throw modifier, or skill modifier. Turning the Undead gets another mod based on undead HD, and attacking adds the targets AC.

I've kept it simple on purpose - originally for faster play at the table and now online. It works, but there are some questions about task difficulty. So ... some options ...

Advantage and Disadvantage
This works by changing the distribution of the d20 roll. Disadvantage is usually handed out when folks are in trouble (you are crippled by poison!) or do describe something amazing (handed out as a reward). It works, but is purely mechanical.

More Interesting Option: Change the Stakes
Changing the stakes of failure definitely changes things.  For example, climbing that 30' cliff could have 3 difficulties based on failure:

• Low: you can't get a good grip and are unable to climb
• Moderate: you'll get stuck part way up and have to check again
• High: you'll definitely fall from 20-30' up (which is 2d8 or 3d8 damage, which is a LOT)

Getting a Critical Failure (Natural 1) increases the failure results

• Low: you are stuck
• Moderate: you fall
• High: one of these: no save for 1/2 damage, 2d4+8 or 3d4+12 damage, automatically break a random limb

Another Option: Succeed with a Cost
I really liked this option in Dungeon World and use it sometimes. Using it all the time doesn't feel right because sometimes things just don't work. A roll fails, but I'll give the player an option to succeed for a cost. Some examples:

• Low: it takes twice the time to climb (time tracking is a big deal in this game)
• Moderate: Cut off your backpack to lose some weight
• High: Lose 1d4 HP to exhaustion; 0 hp becomes 1 hp but you have a sprain and disadvantage to things for a while.