If you're looking for manga similar to Gakuen Heaven: Hamu Hamu Heaven, you might like these titles.
When everyone else possesses the body of a saint, a princess, or a lady (duke’s daughter), I possessed a hamster. Its hobby is to eat squirrel chestnuts. Its specialty is to pretend to be a woolsmith. Soi, who has become a pretty hamster, decided to find an owner to survive. Soi, who captured the sense of an owner, ran back and forth. “Chii (Raise me)”. “...” “Chii (Raise me)”. The man’s eyes shook when he saw the bold hamster. Finally, with cuteness as her weapon, she succeeded in being picked up by a little boy. The hamsters’ life I had dreamed of was cozy. Sunflower seeds, sweet dried strawberries, and fluffy sawdust...