Gladioli almost always need staking, whatever the soil is like.

You might try setting the tall plants deeper into the ground and then hilling them.

Sounds like you do need something to add to your soil to make it more friable, able to take in moisture and retain it. I cant see a bulb coming up and falling over simply because there's no compaction of the soil to any extent.
Sunds more like you're trying to grow something in sand.
For sand, add organic matter which is more generally suggested to be made up of compost to about 30 - 40%. Then add peat moss/sand/and maybe even some potting soil with perlite/vermiculite.

No need to worry about termites in wood mulch...they will not take to living in this medium. Earwigs will though and, because its always damp there, set up housekeeping and a you provide a nice dinner menu with the plants.

Sometimes my glads fall over growing in my sandy soil with about 8 percent organic matter mixed in, so staking is necessary. A soil with 30 to 40 percent organic matter is going to hold way too much water for plants to grow in, that would be a bog, fen, swamp as well as very difficult to attain.