NB: The following list is far from exhaustive and chosen from the point of view of some popularity and availability of information (relevant literature) in English:

• The Last shogun of the Tokugawa Shogunate, TOKUGAWA Yoshinobu (linked to the very basic information in the National Diet Library in English) himself, lived until 1913, so he lived longer than Emperor Meiji (who died in 1912). He is often featured in popular history of Bakumatsu/ Meiji period, and at least one of his biographies (though not academic and written by the famous novelist SHIBA Ryotaro) is also translated into English (linked to goodreads.com's introduction of SHIBA Ryotaro, The Last Shogun).
• Among the ex-ministers of the Shogunate, SHIBUSAWA Ei'ichi (1840-1931) who later became the leading business figure in Imperial Japan had served Yoshinobu in 1860s, though he had not been born in samurai estate (shizoku), but as a son of relatively well-off farmer family. His autobiography is also translated into English: The Autobiography Of Shibusawa Eiichi: From Peasant To Entrepreneur, trans. Teruko Craig. Tokyo: Tokyo UP, 1994.
• While not directly served to the shogunate in 1868, as for how those who had belonged to the pro-Shogunate clan experienced the Imperial Japan after Meiji Restoration, Military Officer SHIBA Goro (1860/61-1945)'s autobiography also has a decent English translation: Remembering Aizu: The Testament of Shiba Goro, trans. Teruko Craig. Honolulu: U of Hawaii P, 1999.

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• One of the most influential figures in Bakumatsu/ Meiji Period, YAMAGATA Aritomo (1838-1922) survived the power struggles in the top strata in Meiji Japan and became PM twice, and kept his influence based on the faction and his power base, the Imperial army, almost until his death. He must have been featured in many literature as a key figure in politics as well as the army in Imperial Japan, among others, the classic, Roger F. Hackett, Yamagata Aritomo in the Rise of Modern Japan, 1838-1922. Cambridge, MA: Harvard UP, 1971.
• TANAKA Mitsuaki, ex-samurai of Tosa Clan and became Imperial Household Minister under Ito Cabinet lived until 1939. He is sometimes mentioned as the "last samurai" in Japanese popular medias. He published a memoir of his experience in Bakumatsu/ Meiji period in his later years (1928), but I don't know whether the memoir is translated out of Japan (the following link is NDL's digital edition of the 1st edition, of of course in Japanese): https://dl.ndl.go.jp/info:ndljp/pid/1173529

(Edited): fixes typo.