ふくよか

丸まる々まる
丸々 is more about being round and chubby, often used for babies or animals, while ふくよか has a softer, more elegant nuance and can describe adults or scents.
豊ゆたか
豊か means abundant or rich in a broader sense (wealth, nature, etc.), while ふくよか is limited to physical plumpness or mellow fragrance.

Written forms

ふくよかUsage100%
Usually written in kana; the kanji forms 膨よか and 脹よか are rare.
膨ふくよか
rarely-used kanji form
Rare kanji form; 膨 suggests swelling or fullness.
脹ふくよか
rarely-used kanji form
Rare kanji form; 脹 also suggests swelling, but this spelling is very uncommon.

Etymology

The word is likely derived from the mimetic root ふく (suggesting swelling or soft fullness) combined with the adjectival suffix やか. The exact historical derivation is uncertain.