Family stress - who should walk me down the aisle?

I’m so excited for our wedding but the one thing that is causing me a lot of stress and anxiety is who should walk me down the aisle? My parents split up on bad terms when I was about 7. Since then they have both gone on to have new partners. I have always had a relationship with my biological dad, but we’ve never been super close. We’ve always spoke, I’ve popped round for a brew, visit on Christmas Day etc but that’s really the limit of our relationship. He’s always been far more interested in my brother than me to be honest. My mum is my hero and my best friend in the world. I also love my step-dad too and he’s probably been more of a father figure to me than my biological dad. He taught me to swim, to drive, drove me everywhere for sports games, etc. Now the question is… who do I ask to walk me down the aisle? I know it is tradition for the father of the bride to do it but it just doesn’t feel right to me and I’ve already had pressure from my mum for him not to do it. But I don’t want to hurt his feelings and I hate conflict so the idea of having this conversation with him terrifies me. I already know I won’t have my step-dad walk me down the aisle as that would be a slap in the face to my dad sat there so I’m my opinion that’s a no go and he completely understands when I have told him this. I would love my mum to do it, but is this really harsh on my dad? How do I tell him? Or am I doing the wrong this and should I just take the easy route and get my dad to do it even though it’s not what I want? Any help and advice would be great. Thank you!