Hiya
Your LFS at times has spare boxes to give out, depending on how generous they are :lol: They also have the heat packs to which are often re usables, you could enquire about those... I get mine from where my hubby works.. so maybe you could go and sweet talk someone at your LFS for some PM me if you get majorly stuck.
You can get round cornered bags, Aqua One do those, and they are good.
And depending on your location, depends on how good couriers are. We use Poste Haste here in Napier, they have been great here. Others use other firms.. I think it is a case of finding out what works for each area
Good Luck!