Dignified Attire on Shabbat
Question
Answer
Hello
As you mentioned in your question, it is an obligation and a mitzvah to honor Shabbat with dignified attire. One should not wear weekday clothing on Shabbat.
This obligation applies even when one is alone at home and not among people, as the honor is for Shabbat and not for the onlookers (Mishna Berura, Siman 262, S"K 6).
However, on the other hand, there is no obligation to sleep in dignified clothing... Therefore, regarding staying before sleep, it is left to the discretion and feeling of each person.
Source
Shabbat 113 - that your Shabbat attire should not be like your weekday attire.
Shulchan Aruch, Orach Chaim, Laws of Shabbat, Siman 262, סעיף 2
One should strive to have beautiful clothes for Shabbat;
Mishna Berura there, S"K 6.