Siman 555
Presented here for study, not as a practical ruling. The Shulchan Aruch rules by Sephardi custom, the Rema's glosses by Ashkenazi custom, and the Kitzur follows Ashkenazi custom. For a practical question, ask your rabbi.
א נוֹהֲגִים שֶׁלֹּא לְהָנִיחַ תְּפִלִּין בְּתִשְׁעָה בְּאָב שַׁחֲרִית, וְלֹא טַלִּית, אֶלָּא לוֹבְשִׁים טַלִּית קָטָן תַּחַת בְּגָדָיו בְּלֹא בְּרָכָה; וּבְמִנְחָה מְנִיחִים צִיצִית וּתְפִלִּין, וּמְבָרְכִים עֲלֵיהֶם.
1 The laws of tefillin and tzitzit on Tisha b'Av, contains 2 paragraphs: We are accustomed not to put on tefillin or a tallit on Tisha b'Av in the morning, but rather to put on a small tallit under clothes, and not make a blessing. And during mincha we put on tzitzit and tefillin and bless them.
ב יֵשׁ מִי שֶׁנּוֹהֵג לִשְׁכַּב בְּלֵיל תִּשְׁעָה בְּאָב מֻטֶּה עַל הָאָרֶץ, וּמֵשִׂים אֶבֶן תַּחַת רֹאשׁוֹ. הַגָּה: וְיֵשׁ לְאָדָם לְהִצְטַעֵר בְּעִנְיַן מִשְׁכָּבוֹ בְּלֵיל תִּשְׁעָה בְּאָב, שֶׁאִם רָגִיל לִשְׁכַּב בְּב' כַּרִים לֹא יִשְׁכַּב כִּי אִם בְּאֶחָד (תּוֹסָפוֹת סוֹף תַּעֲנִית); וְיֵשׁ בְּנֵי אָדָם מְשִׂימִים אֶבֶן תַּחַת מְרַאֲשׁוֹתֵיהֶם, זֵכֶר לְמַה שֶּׁנֶּאֱמַר: וַיִּקַּח מֵאַבְנֵי הַמָּקוֹם (בְּרֵאשִׁית כח, יא) שֶׁרָאָה הַחֻרְבָּן (מָרְדְּכַי דְּמוֹעֵד קָטָן). מִיהוּ עֻבָּרוֹת שֶׁאֵינָן יְכוֹלִין לְהִצְטַעֵר, אֵינָן חַיָּבוֹת בְּכָל אֵלֶּה (תּוֹסָפוֹת). וִימַעֵט אָדָם מִכְּבוֹדוֹ וּמֵהֲנָאָתוֹ בְּתִשְׁעָה בְּאָב בְּכָל מַה שֶּׁאֶפְשָׁר.
2 There are those who are accustomed on the night of Tisha b'Av to sleep spread on the ground and to place a stone beneath their heads. Rema: and these are to pain a person regarding their lying down on Tisha b'Av; if a person is accustomed to lie with two pillows they will lie [on Tisha b'Av] with one. {Tosafot, end of Ta'anit} And there are those people who place a stone under their heads to remember what is said, "He took from one of the stones of that place" (Genesis 28:11) that had seen the destruction {Mordechai on Moed Katan}. Pregnant women, who are not able to cause themselves pain, are not obligated in any of this [Tosafot] And a person should decrease their honour and enjoyment on Tisha b'Av in all that is possible.]