I cant be sure its 'the best' option, but we have
one of these in the van on the front bench (centre position) which leaves sufficient room for a small to medium sized passenger on the left seat. We actually have 3 of these in total in our regular vehicles to save swapping them about all the time, but as they are showing as sold out there they maty have been superseded. Best bet would be to take a tape measure in to anywhere who sell them (we got ours from Halfords) and see what's slimmest!. Oh, bonus info, as the front seats dont have an isofix option, we use outs with a combination of
one of these in addition to the regular seatbelt.