google earth engine - Landsat mosaic with minimum cloud cover over an area of interest

I'd like to create a mosaic with minimum cloud cover over an area of interest. I have done this by using the sort function to return the image with minimum 'CLOUD_COVER' value and am happy with the result.

// Find image at point with least cloud cover in the year 2014

// imported // landsat = 'USGS Landsat 8 Raw Scenes (Orthorectified)'

var trueColor= {
  bands: ['B4','B3','B2'],
  min: 5000,

  max: 15000,
};

var point = ee.Geometry.Point([116.64,8.26])

var image = ee.Image(landsat.filterDate('2014-01-01','2014-12-31')
  .filterBounds(point).sort('CLOUD_COVER').first());

Map.addLayer(image,trueColor,'True Color Image')

I would like to extend this to a wider area but it seems I cannot use the sort function on an imageCollection in this way. I have tried to use a cloud filter function as detailed in this answer, however the result is extremely cloudy Filter Landsat images base on cloud cover over a region of interest

// Find images within an area with least cloud cover in the year 2014

// imported // landsat = 'USGS Landsat 8 Raw Scenes (Orthorectified)'

var trueColor= {
  bands: ['B4','B3','B2'],
  min: 5000,
  max: 15000,

};

var polygon = ee.Geometry.Polygon([
  [[116.64,8.26], [119.41,8.26], [119.41,10.44], [116.64,10.44],[116.64,8.26]]
]);

var collection = ee.ImageCollection(landsat.filterDate('2014-01-01','2014-12-31').filterBounds(polygon));

var withCloudiness = collection.map(function(image) {
var cloud = ee.Algorithms.Landsat.simpleCloudScore(image).select('cloud');

var cloudiness = cloud.reduceRegion({
   reducer: 'mean', 
   geometry: polygon, 
   scale: 30,
   maxPixels: 1e9
 });
 return image.set(cloudiness);
 });

 var filteredCollection = withCloudiness.filter(ee.Filter.lt('cloud', 10));


 Map.addLayer(filteredCollection.mosaic(), trueColor, 'spatial mosaic');