All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
In principle, it is permissible for each of the spouses to look at the entire body of the other.
Bahz ibn Hakeem narrated that his grandfather asked the Prophet "When should we cover our ‘Awrah and when should we not?" Thereupon, the Prophet said, "Cover your ‘Awrah, except from your wife or what your right hand possesses." [At-Tirmithi]
If the husband sleeps with his wife while they are both naked during the day in Ramadan or during the obligatory fast such as when making up for a missed fast and the like, then this exposes them to engage in foreplay, such as touching, kissing, hugging, and putting his penis on her body [without intercourse], and so on. So it is better to avoid it because this is part of the lust for which Allah praised the fasting person by abandoning it as a way of getting closer to Him, as Allah says in a Qudsi Hadeeth: "He abandons his food and drink and desire for My Sake." [Al-Bukhaari and Muslim]
These different kinds of foreplay are not all the same; the most dangerous of which for a fasting person is playing with one’s penis on her body, because this may lead to invalidating the fasting due to ejaculation. This is contrary to the objective of fasting so one should avoid it as a way of fearing to commit what is forbidden in the Sharee’ah.
Playing with one’s penis on the wife’s body may result in his penis touching her vagina without an obstacle. This is forbidden even if there is no ejaculation or penetration. This is not the same meaning as the Hadeeth of 'Aa'ishah, and what the Prophet did with her while he was fasting as he used to kiss her while fasting, and he was approaching his wives intimately but he was the best of the people in controlling himself. But who among ourselves can claim to be able to control himself?
The scholars who gave concession that the fasting person may kiss his wife conditioned that on those who are able to control themselves and who do not fear that this would lead them to what is beyond the kiss. If a person cannot control himself [his desires], then kissing his wife is forbidden to him by the agreement of the scholars.
Abu Hurayrah narrated that a man asked the Prophet whether one who was fasting could embrace his wife and he gave him permission; but when another man came to him, and asked him, he forbade him. The one to whom he gave permission was an old man and the one whom he forbade was a youth. [Daawood]
Allah knows best.