Sending you all my best wishes. What an emotional time of goodbyes and welcoming. I am incredibly sorry you have to say goodbye. [name_f]Mary[/name_f] [name_f]Elizabeth[/name_f] is a beautiful name and I know you will be able to find something wonderful to honour her.
Although [name_f]Mary[/name_f] is traditionally feminine, like a few others have said, there are some masculine names that are along a similar vein.
[name_m]Marius[/name_m] is a lovely suggestion. [name_u]Mars[/name_u] could also be a wonderful nickname for it, or even stand alone is a name in its own right.
If you decided to go for a name that is like [name_f]Elizabeth[/name_f], [name_u]Elijah[/name_u] / [name_u]Eli[/name_u] could be a good option. Some other nice variations of this could be [name_u]Elias[/name_u] or [name_u]Elliot[/name_u].
[name_u]Elliot[/name_u] [name_m]Marius[/name_m] would be absolutely wonderful.
If none of these, or any of the other suggestions feel right, there are plenty of other ways you could consider honouring your mother. Perhaps a favourite city/country of hers? A favourite flower of hers?
(For example, [name_u]Milan[/name_u], [name_u]Paris[/name_u], London… [name_u]Or[/name_u] [name_u]Royce[/name_u], [name_u]Rosario[/name_u], [name_m]Ambrose[/name_m], if roses were her favourite flower)