Good to see the lower bar position is working out. I've always used deep breaths and tensed up my abs between each rep to stop myself leaning forward and keeping my back in check. I have found the cushion of air has kept me folding over, and exhaling as I go back up whilst still keeping my abs tense keeps the weight behind me.
You know... fish, chips, cup of tea, bad food, worse weather, Mary fucking Poppins... London!