It would feel like such a luxury if I could spend some time all by myself one of these days.
I would feel so spoiled if I could just have a little time to myself someday.
この場合、次のように言うと良いでしょう。
ーIt would feel like such a luxury if I could spend some time all by myself one of these days.
「いつの日か自分だけの時間を過ごせたら、すごく贅沢に感じるだろう」
It would feel like such a luxury で「とても贅沢に感じるだろう」と言えます。
to spend some time all by myself で「自分一人だけで時間を過ごす」
ーI would feel so spoiled if I could just have a little time to myself someday.
「いつか自分だけの時間を少しだけでも持てたら、すごく甘やかされていると感じるだろう」
「贅沢に感じる」と言う代わりに甘やかされていると感じる、と言っても良いですね。
to have a little time to myself で「自分だけの時間を少し持つ」
ご参考まで！
カナダ 
