Pull out one of your existing bulbs. The base is either wedge shaped (T10) or round bayonet (like a 1157, if memory serves). Order LEDs with the same type of base.
Any LED under 200 lumens should provide noticeably less light than your incandescents, I think. A typical 1157 incan is about 400 lumens.
2700K is yellowy light similar to incans, 3000-4000K is whiter but still has a bit of warmth. Anything higher color temp than 5000K starts to look sort of blue and harsh IMO.
If you insert an LED into the socket and it doesn't light up, usually you need to take it out, flip it over, and reinsert it. They tend to be more directional about their current flow than an incandescent.