Chapter 5 of the 2002 General Instruction of the Roman Missal (GIRM) has the title “The Arrangement and Furnishing of Churches for the Celebration of the Eucharist”. It is
at usccb.org/liturgy/current/chapter5.shtml .
Perhaps useful in this case would be:
“308. There is also to be a cross, with the figure of Christ crucified upon it, either on the altar or near it, where it is clearly visible to the assembled congregation. It is appropriate that such a cross, which calls to mind for the faithful the saving Passion of the Lord, remain near the altar even outside of liturgical celebrations.”
And: “318 … Thus, images of the Lord, the Blessed Virgin Mary, and the Saints, in accordance with the Church’s most ancient tradition, should be displayed for veneration by the faithful in sacred buildings and should be arranged so as to usher the faithful toward the mysteries of faith celebrated there. For this reason, care should be taken that their number not be increased indiscriminately, and that they be arranged in proper order so as not to distract the faithful’s attention from the celebration itself.” (I have removed two footnotes.)
Perhaps this part may help (in a discussion of what is distracting): “303. …In already existing churches, however, when the old altar is positioned so that it makes the people’s participation difficult but cannot be moved without damage to its artistic value, another fixed altar, of artistic merit and duly dedicated, should be erected and sacred rites celebrated on it alone. In order not to distract the attention of the faithful from the new altar, the old altar should not be decorated in any special way.”