#Use a Luckstone Following from your comment on Pyrotechnical's answer, if you want to increase skills and saving throws only but do not want to affect spells, HP, and all the stats of all the NPCs and monsters, what you're effectively looking for is a +1 to all skills and saving throws.

Instead of changing how the rules work to suit this need, how about just hand out Stones of Good Luck? This item does exactly that. If it's acceptable for them to all have an Uncommon item that uses up attunement slot, this may be an easier solution (or just say that everyone gets 4 attunement slots, or just houserule that this item doesn't require attunement after all).

Use a Luckstone

Following from your comment on Pyrotechnical's answer, if you want to increase skills and saving throws only but do not want to affect spells, HP, and all the stats of all the NPCs and monsters, what you're effectively looking for is a +1 to all skills and saving throws.

Instead of changing how the rules work to suit this need, how about just hand out Stones of Good Luck? This item does exactly that. If it's acceptable for them to all have an Uncommon item that uses up attunement slot, this may be an easier solution (or just say that everyone gets 4 attunement slots, or just houserule that this item doesn't require attunement after all).