Goldie,

I think you are on a hiding to nothing if you cannot see a badge or shoulder flash. The only thing the uniform might tell you is whether he was commissioned or not, assuming that you cannot see any stripes. At the risk of being shot down (sic), officers in the trenches wore their rank on their sleeves (as Edmund Blackadder and his sidekick did in the TV series). Baldrick had nothing on his sleeves! (There must be a witty comment there, but I am damned if I can think of one).

However, if you know your man died in Jan 1918, have you tried the Commonwealth Graves Site. Against his name should be the regiment/unit in which he served and then you can follow up with the Regimental Museum and the War Diaries in the PRO.

James