When you're touching another person, you feel warm.
When you're right next to someone, you can feel the warmth of their body.
ーWhen you're touching another person, you feel warm.
「人とくっつくと温かい」
to touch another person で「ほかの人に触れる・接触する」
to feel warm で「暖かさを感じる・ポカポカする」
ーWhen you're right next to someone, you can feel the warmth of their body.
「誰かの真横にいると、その人の体温の温もりを感じることができる」
to be right next to someone で「人の真横にいる・すぐ横にいる」
to feel the warmth of ... で「…の温もりを感じる」
ご参考まで!