The OSR crowd generally frowns on skill systems, with the exception of LotFP. I understand the concerns about player immersion and seek ways preserve that. Likewise, I have friends that cringe at the absence of something under the hood.
Some people will cry out "D20!", but think of these guidelines like armor classes. Filthy ascending armor classes. If your adventurous, make a chart with a repeating 20 like the AD&D attack matrices so the system scales more gracefully.
What to roll:
- Regular Tasks: D20 + Skill bonus vs 10 (like an unarmored guy of AC10)
- Challenging Tasks: D20 + Skill bonus vs 15
- Hard Tasks: D20 + Skill bonus vs 20 (like hitting someone with platemail and a magic shield)
- Impossible Tasks: D20 + Skill bonus vs 25
How do I get a skill bonus:
- Class skills: Equal to your level. You class provides one of more class skills. You never spend points on these. The skill bonus is always equal to your level.
- Secondary skills: Start at 3, requires a skill point to increase. These are minor skills from your past or upbringing. Roll on the DMG table, choose Education or a Tradecraft. You can only increase them by spending skill points.
- Other skills: Start at 0, requires a skill point to increase. Everything is an "other" skill. You spend a skill point to gain a increase their bonus. The skill bonus can not be higher than your level.
Here's a draft skill list:
Animal Handling - Riding, training, controller animals
Athletics - Running, swimming, jumping
Coordination - Dodge, balance, acrobatics, juggling, dance, knots, ropework
Diplomacy - Leadership, Negotation
Education- history, geography, reason, philosophy
Folk Lore - creature lore, regional lore, geography, superstitions, local customs
Insight - includes detect lies, estimate sums, evaluation, gauge opponent
Survival - encompasses hunting, fishing, foraging, nature lore
Tradecraft (specify type) - smithing, carpentry, jewellery making, brewing, engineering, performance