Two come to mind immediately: Mr. Knightley (which you could tell from his name) and Mrs. Weston.
For examples, I don't want to give answers away, but you can imagine a time when a lady was judged by the respect given her by "people of worth and respectability." A character who looks out for avoiding quarrels and unwarranted antagonism between others, and overlooks the little errors others make, is a character who shows sense and self-restraint. Harriet and Miss Fairfax both benefitted from sense & self-restraint of the two characters I named above.
Consider what might have happened to Hariet socially if no man had asked her to dance following Mr. Elton's open aversion to the offer?
Consider what might have happened to the relationship between Mrs. Weston and Emma (as well as Emma's father...and the respect of Emma's family name) had Mrs. Weston ever pointed out Emma's father's tendency to fear illness...or to point out her married name repeatedly to him? What impression might others have had of them?
You may want to check the scene in which Emma discovers Mr. Churchill's secret engagement, which she realizes may subject her reputation to embarrassment. Miss Weston is pro-active to settle the matter and calm the sense of injury in Emma. Had she not done so, and had Emma chosen to shun Miss Fairfax (even more), Mr. Churchill, Mr. Weston...they and even Miss Bates could have suffered social disapproval as a result.
Happy searching! Emma is a fun read!
There aren't too many, that's for sure. The most obvious one would be Mr. George Knightley. The other characters may have some flashes of "sense" from time to time, but none of them could be said to be defined by sense and restraint to the extent of George Knightley.