Shouldn’t have to buy additional hardware for this.
You’d never export only one Field. You’re exporting Interlaced, so you will have to choose which Field has dominance (HD has Upper Field dominance; SD has Lower Field dominance). You make that selection in your Export Settings dialogue box.
Make your Sequence Settings match your footage & your Export settings should match what your delivery specs. If you want to confirm which Field has dominance, use MediaInfo.