I have just managed to get a 'Cars' dressing up outfit for DS1 at H&M online for £1 + postage (so £4.90 total) - original price £16
There are 2 codes - one for £5 off orders over £11 which is 1304, the other is for 25% off your most expensive item, which is 0241. What you can do, cheekily, is to put an expensive item in your basket which you don't necessarily want, apply discounts, then remove item, so you still get discount. You must pay by card (default option is pay by invoice) or your order will have to be a minimum of £6.