Ive got a skinny DD who currently in teenfits.
Haven't got any easyfits so can't help you on those - but have 1 BG v3.
On the smallest rise setting, with the larger booster (coz she's a heavy wetter even at 8 weeks!!) it fits well.
the overlap on the tabs is great for getting a good fit on her skinny thighs!
(our DD was 4lb 11oz born, now 7lb 15oz at 8 weeks - but also long and skinny)