Filter or sort hits to get one with special flag

[ov7a]

I have a query like this.

{
  "size" : 0,
  "query" : {
    "constant_score" : {
      "filter" : {
        "bool" : {
          "must" : [
            {
              "term" : {
                "field1" : {
                  "value" : "value1",
                  "boost" : 1.0
                }
              }
            },
            {
            	//... some other filters
            }
          ]
        }
      },
      "boost" : 1.0
    }
  },
  "aggregations" : {
    "field2-agg" : {
      "sum" : {
        "field" : "field2"
      }
    }
  }
}

I want to also obtain single element with field3 = true.
One way to do this is to make a bulk request with 2 requests: this and a copy of this with additional must closure and size 1. But this would result in executing the same query twice.
Another way is to add a top_hits aggregation with custom sorting by field4. But sorting is expensive.

Which variant would be executed faster? Is there more elegant way to do this?