@ joerookery.
Hi Joe,
We always do our battletrips on our own. I plan the trips with maps some months before.
Nowadays, I thought since 2005, there are 2 battlefield travel guides about the Western Front, North and South, with excellent schematic battlefield maps and pictures of the famous Major & Mrs Holt. They also launched a battlefield guide about Gallipoli. Even at home these guides are very pleasant to read! These guides and maps saved me a lot of time for planning my trip of last spring! I throw in a link for you about these battlefield guides. Click here:
LINK. I just ordered also their battlefield guide today about Operation Market Garden of the 2nd World War in the Netherlands.
But if you prefer to go with an organised tour, I don’t have any experience myself. I do know that most battlefield tours are organised for obvious regions in the regions were the British Troops were active: Ypres and the Somme. In towns like Ypres (Belgium), Albert or Peronne (France) these battlefield tour companies, mostly run by English people, have offices where you can make reservations.
Your wheelchair is no problem visiting the most of the large cemeteries and important sites. Especially in France these sites are accommodated with asphalt paths with exception of Beaumont Hamel (gravel paths). Some spots on the battlefield may alas be just viewed from a distance, because sometimes the mud can be as annoying as 90 years ago. But this is also an obstacle for a guy, walking with a stick like myself.

I would suggest: always bring a nice pair of binoculars, and a compass. For each battlefield you need at least 3 days.
In France the accommodations on the sites are modern and most of the time, it seems to me, wheelchair friendly. But I don’t know for sure. If you are not living in one, like another friend of mine, you don’t realise all the time about these accommodations, until you are confronted on a trip together with unexpected difficulties this situation could rise.
If I can be of more specific help, please email me or perhaps open a new topic about travelling tips, Joe, in which I would gladly contribute, where I can.
Many words, Joe, to tell you, I am sorry, I don’t have any experience myself with battlefield Tour operators.
But I do hope you will appreciate my tip about the travel guides of the Major & the Mrs. :?
Pierre GG