From the long, long trail:
KOYLI 1st Battalion
August 1914 : in Singapore. Returned to England and landed at Southampton on 9 November 1914.
9 November 1914 : moved to Hursley Park and on to Harwich on 18 November.
17 December 1914 : returned to Hursley Park and attached to 83rd Brigade in 28th Division.
16 January 1915 : landed at Le Havre.
26 October 1915 : sailed from Marseilles for Salonika, arriving 7 December.
20 June 1918 : left the Division and moved to France, landing at Taranto (Italy) 2 July 1918.
16 July 1918 : attached to 151st Brigade in 50th (Northumbrian) Division.
http://www.1914-1918.net/koyli.htm
His medal card on Ancestry says he entered France on the 15th January 1915, maybe as part of the advance party for the rest of the battalion. I couldn't find any pension records or anything like that.
They were quite close to the PPCLI on the 8th May; Lyn Macdonald focusses on the Canadians (and the Suffolks) in her book 1915 (pp. 287-290), but it will give you a flavour of what they went through. The King's Own are mentioned. According to her, part of the 83rd Brigade front gave way in the German attacks on the 8th May. They seem to have been close to the Suffolks, somewhere North of the Frezenberg-Zonnebeke road. By the time your man died the battalion was already down to around 300 men (from about 1000). It was a bad time.