It's only hard if you look for the perfect pot- and if you look for a "pot"!.. Really only width is important- and not even that important...
I have all kinds of take out containers upside down/right side up, cut down plastic cups, even a hand full of pony beads set in hot glue to get inside pots to the right height to match the outside container (with a bit to grab) and don't sit in standing drainage water...
the height is really important to get the drainage done- but you can shove anything that stands up to water in the base of a planter, I like to melt hot roofing nails (wide head) through a take out pint container as a base inside my pretty ceramic pots. Solo cups are my best friends becasue I can cut them to support the inside pot just 1/4" higher than the container rim... as long as there is some drainae gap -
Okay- yes- this is nuts- but it only takes 20 minutes and a garrage full of stuff you should have thrown out 20 years ago....
Ohhhh... right.