My mobile has shit ergonomics and poor responsiveness (shutter lag, autofocus, bloated OS).

Anyone already got something they'd recommend, or any thoughts to toss into my mental melting pot?

I'm not too fussed budget-wise - something suitable should really be possible for £200 or so, but I accept it'll be more, though if it reached four figures I'll probably not bother.

I briefly looked at RX100 range earlier but the reviews suggested Panasonic's equivalent had the edge, though I've yet to checked in terms of what criteria that is.

Looking at the RX100 range you're right there'd definitely be no advantage in mk4, and even comparing mk3 to mk2 it's not clear if there's £160 worth of difference (£85 after cashback at Wex).

The mk3 does have a newer processor and ND filter which may help prevent blown highlights.

There's also the Canon G7 X mk2 which is similar price and features, and the Panasonic Lumix TZ100 which is better in some ways and worse in others. No doubt combining the three would give me just what I'm after. :/

Anyhow, the Panasonic TZ100 is what I went for - controls felt better - similar to what I'm used to from Nikon, even if actual operation is something I'm getting used to; a lot of functionality and options crammed into relatively few controls, but it does appear to be sufficiently customisable, and the viewfinder is acceptable (no EVF is good, compared to optical, but it wasn't as bad as the review suggested).

If you want examples of what I can do with it, you'll have to wait.