Whilst in principle radish are easy, sow the seed, remove the weeds, pick them, a lot of people just can't grow them, so you are in good company. They are fussy.

Calling them cool season depends where you live and what variety you grow. Here in England I find sowing them too early in the spring it's too cold, they don't grow fast enough and so become small and woody. The Japanese grow some amazing radishes, and clearly the Japanese varieties are suited to a warmer climate.

They do need a reliably moist, reasonably fertile and water retentive soil to grow well. If you have cabbage fly, they'll attack your radishes. Being brassicas, they do need sufficient lime in the soil or they won't grow.