I agree with your proposal. The current system of obtaining crop seeds is unrealistic and not enjoyable.
However, if acquiring seeds becomes easier, agricultural production could increase explosively, making the game too easy. If this change is implemented in the game, additional labor or resources should be required for farming to maintain balance.
Here is my suggestion: pests and disease
If there are too many of the same type of crop within a certain range, pests and diseases may occur. Randomly selected crops will become infested, changing appearance and reducing yield. If the infested crops are not removed quickly, the infestation will spread to adjacent crops.