After a few rides I’ve realised that the backsweep on my bars just isn’t big enough and i get pinching between the joint of my thumb and my wrist.

Are there any handlebar grips that add a bit of thickness as they go out (taper towards the stem) that would add a bit of effective sweep?

Try riding really hard between a couple of narrow trees 😉

Ergon grips do in various levels. Ge1 might be best, but they are £30 so unless the bar is super uber posh then swapping it out is probably a better choice. Ppresuming of course you have tried rolling it back a little first to increase backsweep in preference to upsweep.

Your best bet is to try a Ergon grips. They do a variety of shapes. Some give you an artificial sweep which may help.

Edit: Slow fingers. I’d also opt for a new set of bars. Stooge Moto and cut down?

There are some ESI grips that have a bit of taper in them.

Standard ESI come in Extra chunky, chunky and racer’s edge

“FIT CR” or “FIT XC” are blends – Cunky and racers edge, or XtraC/Chunky

Wider on the outboard side.

http://www.esigrips.com/fit-xc-grips

Another grip option:

BG Contour grips