Mounts are commonly used when framing works of art on paper including photographs, drawings and watercolours. Anything on paper needs to be kept away from the glass to avoid moisture damaging the paper. Air needs to circulate to ensure the longevity of all artworks on paper. Mounted pictures in frames are designed to offer protection from acid but not to be air tight.
The average width of mountcard surrounding average sized artworks varies between 40 mm and 55 mill. This convention is established so there is ample space to appreciate an artwork and to avoid it appearing hemmed in.
Conventions are there to be broken. Mount widths can be cut any size. Each artwork or photo is a unique world and needs to be considered irrespective of convention.
Obviously increasing the surrounding width of a mount will increase the overall size of the frame and push up the cost and this always has to be factored in.
If your drawing is not of great value you may wish to frame it without a mount, not only to keep the cost down but in many cases it is not necessary and may seem like overkill to include a mount. The basic rule is that any artwork of sentimental or monetary value needs to be kept away from the glass.
If you still do not wish to include a mount you could have small spacers fitted to keep the artwork from contact with glass.