PSR's comparison page will give you some idea, place your mouse pointer over each figure to see the manufacturer. Your French infantryman from the 6066 set is on the far right of the second picture.
http://www.plasticsoldierreview.com/ShowFeature.aspx?id=22As you can see the figure from HaT's 1808-1812 infantry set looks a pretty good match but this set does have the earlier pre bardin style uniform.
I would agree that Zvezda's Old Guard and Elite Voltigeurs are probably a decent match but be aware that Zvezda's French Line Infantry is a reissue of the older Italeri set that is shorter and more slender looking.
I think Emhars French infantry might match well enough, PSR lists them at the same height and they look to have a similar chunky style but I don't have these figures so I can't say for certain.
The comparison pic for British line infantry on the PSR link doesn't have a figure from the 6095 set but you can get an idea by comparing the figures to the French infantryman.
Most of the other figures are of the smaller and more slender style. For fleshing out your British army Italeri's Scot's Infantry (that's "scots Infantry" not the ones marked "Highlanders" or Grenadiers") and 95th Rifles sets are both in the newer tall and chunky style.
Again I think the Emhar British infantry might be a similar size.
It's up to you but you could try putting the taller and shorter figures in different battalions to see if the size difference still bothers you.