I peeked at your city on US4.
The first thing I see is that you have all 3 types of t1 factories. Are you trying to PRODUCE all 3 types of sentient goods? If so, that's the first thing to change - that isn't sustainable. Seeds, as you point out, are too expensive to use them on unboosted goods.
It looks like your sentient boost is for platinum. You're in luck - that's typically in demand on US4. You should produce ONLY platinum and trade for it. Since it's worldwide trading and that good is wanted, you should be able to trade easily at 2 stars for moonstone and tree gum.
You can also use magical manufacturing spells on your sentient factories to boost production.