For a leather field holster I would suggest two products made by Galco.
One would be their Dual Position Phoenix. It can be worn strong side or crossdraw. It's heavy leather and suede lined. It carries very well.
The other would be their F.L.E.T.C.H. model. It has a thumb break. I figure it might be helpful for retention while working.
http://www.lightningarms.com/products.htm
Lightning Arms in Oregon is one of the best companies out there for gun leather. Check them out.