No mother of the bride

Well all of them invited, even mum's friends husband. That's the easy part! You could have both your step mother and stand in mother sit with the family.
You could get a photo of your mother and have her friend carry it, or put it in a locket, there's also these little photo frames on a ribbon that they tie to bouquets to memorialize people, your stand in mother could hold a special bouquet with your mother's photos tied to it.
You could do a mother's photo with each of them and one together.
Where this is your wedding I am sure both women will understand not having your actual mother there is hard no matter how long it's been and should be kind to you.
How involved you want each of them in the pre-planning is all about your comfort, you could bring both of them to the first fitting if you want to be inclusive.
If your step mum is just okay relationship wise with you she might not think to throw a shower or anything so you could plan it with the stand in mum.
I think your mother would proud of you regardless and be glad you're being such a thoughtful person to both of these women. It's very admirable.

I just wanted to offer some support, my FH has lost both of his parents now - his mother when he was 13 and his father just before we met. I can only imagine going through this without my mother and my heart goes out to you. I think it's very sweet of you to incorporate both your step-mother and your mother's best friend in your wedding, and I think it's a lovely idea to ask your mother's best friend to step in for the roles MOB would normally take - like getting ready with you and zipping/lacing you up. It sounds like you two have a close relationship and I think she would be honored (and it absolutely will not replace/cancel out your own mother! To me, it would help reinforce your mother's presence because you both carry her memory and love inside you, and you should be surrounded by those you love who love you on your day).Kelly had some great suggestions about ways to include your mother. There are also tons of ideas for memorial tables and ways to incorporate loved ones who have passed on Pinterest. My FH and I talked about reserving seats in the front where his parents would sit if they could be with us. I hope you have a beautiful wedding, congratulations and best wishes!

My mother also died when I was 15 but however, I loathe my stepmother anf she constantly oversteps boundaries.
I was adopted at 16 into another family so my adopted mother is playing the role of mother of the bride despite the fact that I only lived with her for one year but my biological father (who's much better now- just has trouble walking) is still playing the role of my father.
So in short
Mother- gone
Stepmother- helping with vendors so she still feels important
Bio dad- is being my dad, walking me down the aisle and such
Adopted mom- mother of the bride
Adopted dad- moral/financial support

I hope that helps at all! I'm sorry you also had to go through this hard experience