what makes you think it is the size of the hook that is causing you to lose fish? As if that is the case then why use a smaller hook? I would use a larger hook, say a size 6. Just make sure that the hook is sharp (see if it bites into your nail), and also the placement of the hair and you could possibly try a different shaped hook as i cant really comment on a kurv shank hook as i have not used them, i use the korda hybrids with a bit of silicone tubing to give that slight angle to help the hook turn. Just something you could try.
Also at what point are you losing the fish, just after the take, mid playing it or at the net? And the fish that you do land where would you say that the fish is hooked? top, bottom, side, deep or just on the lip? Slight alterations to the hair will make the hook catch in different positions on the lip.