You could install conky
save this to a file...
# Static and Variable Values used by Habitual/John Jones# Static Valuesown_window yesown_window_transparent yesown_window_type desktopown_window_hints undecorated,below,sticky,skip_taskbar,skip_pagerdouble_buffer yesuse_xft yesdraw_outline nodraw_borders nouppercase nodraw_shades nodraw_shades yesdouble_buffer yesborder_width 0text_buffer_size 2048default_color whiteupdate_interval 1.0# Variable Values # These values are the ONLY thing that change from widget to widgetalignment bmgap_x 5gap_y 44minimum_size 50 1maximum_width 100TEXT${desktop_number}run it in Xfce. (terminal) -> with conky -c /path/to/file &
icon/launcher conky -c /path/to/file
Everytime you switch desktops, the number of the desktop will be on the screen.
the "alignment bm" value controls desktop placement. bm is bottom-middle.
See http://conky.sourceforge.net/docs.html for DOCs.