Going for "warmer" and "more sustain" can be kind of opposite goals. Gut and "gut-like" strings are usually warmer, but with less sustain. Some synthetics, like Evah and Obligato can give you some of both, but it depends on the bass. Spirocores are one of the most widely used strings, they have very good sustain, and if you can put up with a few weeks of brightness, they will develop warmth, plus they last for years. I recently played a Kay with Spiros that sounded great. Helicore Orch. is a good arco string, and not bad for pizz on some basses, but will probably lack sustain, especially on a plywood bass. On a good quality bass, gut can give you warmth and sustain. On a Kay, they'll give you some nice punch, but not much sustain.
They fact is you'll have to experiment and spend $$. I'd get a set of Spiros and wear them in.