First of all, I'm heartbroken to hear of your loss. I'm so so sorry to hear such a terrible thing has happened to you. I can't imagine how much it must hurt your right now.

{{HUGS}}
Secondly, I think you have a lovely idea to honor him and I'm sure he's smiling down upon you.
I'm not sure where you're from, but my county webpage lists what is necessary to change a name. You have to fill out certain paperwork to be seen before a judge to grant your request to change. Once he/she does (why wouldn't he???) then you just fill out a few more forms... plus there may be a charge.
Good luck to you.