Answer: The Gemara (Menachot 32b) states: “Rabbi Chelbo said: ‘I saw that when Rav Huna wished to sit on a bed on which a Sefer Torah was placed, he would move the Sefer Torah to a different location and only then would he sit down.’” This means that Rav Huna was of the opinion that one may not sit on a bed on which there was a Sefer Torah. Indeed, the Talmud Yerushalmi states that one may not sit on a bench on which a Sefer Torah is placed. The Gemara recounts that Rabbi Eliezer once (inadvertently) sat on a bench on which there was a Sefer Torah and when he realized this, he immediately jumped up and recoiled as one would as though he had seen a snake (because of his fear and out of respect for the Torah). Based on this Yerushalmi, the Rambam, Ra’avad, and other Poskim rule that one may not sit on a bed or bench on which a Sefer Torah lay.
Maran Ha’Bet Yosef (Yoreh De’ah, Chapter 282) quotes the words of Rabbeinu Mano’ach who writes that some say this only applies to a Sefer Torah, however, other Sefarim do not share the same law; it is nevertheless worthy to act stringently. The Orchot Chaim writes that one should not act leniently so that one does not appear like he is treats Sefarim lightly. Maran Ha’Shulchan Aruch rules stringently only with regards to an actual Sefer Torah, however, the Rama rules that the same applies to other Sefarim.
However, the Poskim write that there is greater room for leniency regarding our Sefarim, for Sefarim which are printed have less sanctity than those which are hand-written. Although Sefarim nowadays require Genizah (ritual disposal) and must be treated with respect in that one may not walk around undressed in a room with a library of Sefarim or change a baby’s diaper when facing Sefarim, nevertheless, their sanctity is not as great as hand-written Sefarim.
After discussing the words of the Poskim regarding this matter, Maran Rabbeinu Ovadia Yosef zt”l rules that, halachically speaking, one may act leniently regarding printed Sefarim. Nevertheless, the Ashkenazi custom is to act stringently based on the ruling of the Rama who states explicitly that one must act stringently regarding other Sefarim as well (and not only a Sefer Torah); they must therefore act stringently regarding printed Sefarim according to their opinion. However, according to the Sephardim who follow the rulings of Maran who rules stringently only with regards to a Sefer Torah, acting stringently with regards to hand-written Sefarim is surely sufficient but there is room for leniency regarding printed Sefarim.
It is nonetheless improper to place Sefarim on a bed on which one sleeps especially when there is concern that a Sefer may fall off during the course of the night and lay on the floor disrespectfully. It is likewise forbidden to place one Tefillin bag on a bed on which one sleeps next to one’s feet, for this is extremely disrespectful; however, if one wishes to place the Tefillin on the bed not next to one’s feet in a way that there is no concern that they will fall off in the middle of the night, one may place them on the bed when one is sleeping in it alone (see Shulchan Aruch Orach Chaim, Chapters 40 and 140).
Summary: One may not sit on a bench on which a Sefer Torah is placed. The Ashkenazi custom is to act stringently regarding all Sefarim. The Sephardic custom, on the other hand, is to act leniently with regards to printed Sefarim; regarding hand-written Sefarim, however, it is preferable not to sit on a bench on which such Sefarim lay.
It is permissible to sit on a bench on which a Tefillin bag lay, however, it is forbidden to place a Tefillin bag on a bed on which one sleeps next to one’s feet, for this is disrespectful.