the synchros will make it difficult for you to shift into 1st if there is any movement in the car at all. if you are still rolling just use 2nd. if you must shift 3rd to 2nd, try rev matching. shift into neutral, let out he clutch, rev the engine up to the natural rev for 2nd in that particular speed, then shift straight into 2nd. takes some practice to do quickly but you will find if you do it right, it will shift straight into 2nd without any resistance at all. and it will save your synchros down the track.
also, i don't see how the floor mats would affect your shifts
hope this helps