My current reportoire of materials used are all artists grade and normally stable under regular conditions according to the manufacturer, they include:
Oil Paint on canvas and board.
Soft Pastel on grit paper.
Watercolour Paint on watercolour paper.
Charcoal on grit paper.
Mixed-Media drawings on heavyweight cartridge paper.
Generally speaking my sizes of drawings and paintings range from ISO (UK):
A5 - 21.0cm x 14.8cm: Generally only good for Mixed-Media studies.
A4 - 29.7cm x 21.0cm: Useful for Watercolours.
A3 - 42.0cm x 29.7cm: Great for Soft Pastel, Charcoal and Oil.
A2 - 59.4cm x 42.0cm: More for my statement pieces in Soft Pastel, Charcoal, and Oil.
All sizes quoted are as unframed, but when a frame is desired I normally do it myself. I usually buy:
Natural Wood frames with no finish to it.
Mount Board of a standard grade,
Hardboard Backing Board,
Fittings if needed,