Rear ported speakers only need space (12"-18" is usually enough) from the rear wall. But I absolutely agree you'll do great things with bookshelf speakers and sub(s).
Due to the square shape of your room, try to add as many big, fluffy, blankets/pillows/couches whatever to tame the bass resonances that will naturally occur due to your room dimensions.
If that doesn't cut it, you may want corner absorption products.