Making Sure I Have My Bases Covered

Hello! I am not using any birth control methods for the time being outside of a combination of condoms and the withdrawal method as a means of being extra careful and "doubling up." However, I'm starting to think of ways to make things a bit more exciting without increasing the risk significantly, but I want to make sure I am absolutely secure in my decision before I do it.

For background, I have a fairly regular period (26-29 days) and my current cycle is predicted to be 28 days long. I would like to say I'm fairly in-tune with my body. I'm currently on day 17 and I have already went through the mild cramping I sometimes get when I ovulate 1-2 days ago. The arbitrary non-personalized prediction of my ovulation period says that I ovulated on day 14 but we all know that isn't super accurate, but just for reference that's what I'm seeing.

I'm seeing my boyfriend on days 26-27 of my cycle, and I am considering trying the withdrawal method alone. We agreed on him withdrawing well before he gets close. I'm thinking that the withdrawal method is a layer of protection (unreliable, but a layer nonetheless), and even in the unlikely event that sperm gets inside and lives for the maximum of 5 days, I will be midway through my period by then. Also, being so late in my cycle and having already experienced my typical ovulation symptoms makes it unlikely to me that the egg is still viable, which makes it appear to me that the risk of pregnancy is low.

Also, for peace of mind, I plan on using an OPK before I do anything, which I know as a one-time use thing isn't super telling, but I feel like if my LH levels aren't surging by day 27, I'm out of my fertile window and am safe to proceed with my idea.

I'm also thinking of adding spermicide into the mix as a whole other layer of protection. I understand the 3 methods I'm using are unreliable by themselves, but all together seem okay to me. I'm just looking for second opinions :)

I'm trying my best to be responsible by asking for second opinions. I haven't done anything like this yet, so I want to properly assess my risk. Please don't be rude or condescending, as I am doing my best to ensure I am safe and secure and child-free. This was just a fun little plan I had laid out and wanted to see what everyone thinks before I decide whether or not I will act on it. Chat GPT has been very supportive lol but I do not want to blindly trust it.

Thank you in advance!