There are many synonyms that can be used in place of the phrase "thought sentimentally." Some options include: reminisced, reflected emotionally, mused nostalgically, pondered fondly, considered with affection, and contemplated sentimentally. These synonyms convey the idea of thinking about something with a deep emotional connection, often involving memories or personal experiences. They are useful for expressing a sentimentality or nostalgia in writing or conversation. However, it's important to remember that different words carry slightly different connotations, so it's important to choose the one that best fits the intended meaning and tone.