Carpets in houses where young children live get minging. That's normal. Do a once-every-six-months hire of one of those industrial washy vacuum cleaner things (oh what the heck are they called????) and the rest of the time, don't sweat it. Little children drop things, generally without thinking "now, how can I make my mother really angry???" first. There's no point sweating the basic hygeine one, IMO (but I am a complete slummy mummy)
Weeing in odd places - what twiglett said.
crawling on floor in tescos - whyever not? Take some time to lean on your trolley and watch the world go by, meet the eyes of other people passing and say cheerfully "ah, it's all machine washable!" and "amazing how fascinating other people's dust is!" and things like that. (Yes, I'm usually the mummy down on the floor with the small children, going "oh yes, I see, what an interesting shadow!" and other such inane comments, but it keeps us all happy and that's the main thing)
And it sounds to me like your Ds isn't totally invested in pottying yet. Ask him, in a nice way, if he'd rather be in nappies so he doesn't have to remember to use the loo. Or of he'd rather be in nappies at certain times of day. Or he could wear one just for insurance, but try to use the loo when he remembers. There's no point hurrying that process along - when a child is ready, then they are ready, and they are the ones who know it.