I don't see the need for titles in life generally, but especially for buying things.
I think it is better to go with no title at all or, failing that, if people insist on wanting a way to discriminate against people for the sake of it, I prefer the bare minimum of Mr / Ms.
Equality between men and women in this issue is signified by giving equal options to men and women. The options need to be equal in terms of status and number.
Mr / Mrs - is unequal because of status.
Mr / Mrs / Ms - is unequal because of status and number of options.
No title - is equal because of status.
Mr / Ms - is equal because of status and number of options.
Mr / Mss* / Ms /Mrs - is equal because of status and number of options.
*Until a new option (I suggest it could be "Mss") is introduced for a man who wants to publicly declare his pride in being married to his wife, use of Mrs for women is unequal. How many men would take up such an option? Probably none. That, in itself, would highlight the inequality of Mrs.