Interesting problem - I wonder if anyone makes a silicone bread tray with a reinforced wall - looks like there could be a gap in the market for such a product.
It seems a pity to have to use a metal tin as well, plus, presumably you need to match the sizes up.
I would have thought putting a silicone mould into a bread tin would have reduced the thermal efficiency - but having never tried it, I don't actually know.
It sounds as if a mesh metal cradle would do the job ok - if you feel a bit adventurous, I would suggest buying a cheap metal mesh cake-stand (the sort of thing you use for cooling cakes on) and bend it into the shape of a cradle. Use a table or a worktop with a nice square edge and make your folds using the edge of the table as a former - i.e. with the mesh laid flat on the table just push downwards so that the material bends over the table edge. At a guess I would think the ends are not such a problem, so perhaps an open ended cradle would do the job - much easier to form up.
I use ordinary non-stick bread trays and they don't seem to stick - the walls slope outwards and the corners are rounded which seems to help.
If you are looking to buy some new trays, I recommend TK Maxx - they sell good quality trays at very reasonable prices.
These posts have put me off using silicone bread trays, because quite honestly I can't see the point.
If sticking is a problem then I would have thought adding a home made silicone liner would be cheaper and probably better - lidl's had sheets of silicone in their offers last week - they will probably still have some, can't remember the exact price but it was very cheap.
Also, Lakeland do a custom built liner, but a little more expensive - although they say they are reusable.