I've a solution for your issue.
1. Don't bench. It's the best solution
2. It's really simple actually. If you don't have 1.25KG plates, do this. Say M/W/F. M-100KG. W-102.5KG F-105KG. Since you don't have 2.5, just do M-100KG, W-100KG, F-105KG. For dumbbells, it's probably not as simple to do, so go by feel. Do the 5x5 as well, then supplement the supporting muscles to strengthen the movement.
Or even easier, use a 3 day back/chest/leg split.
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Squat Solution:
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It's pretty easy actually your issue with the squat rack. DO zercher squats. I used to wrap a towel around my arms to do them when the weights got heavy. Then I got smarter, and bought 2 PVC pipes, and cut it right in the center.

I'd open these pipes slightly and slide it into the bar and put my arms in there when doing Zerchers. It did slip and slide a bit, but that was part of the process of learning to use it. Then when it got tougher my arms, I just stopped using the pipes. I've gone up to 140KG doing Zercher squats, so nobody can say they can't go heavy doing Zercher squats. If you can't, means you just gotta get stronger.
Here's another bonus of the Zercher squats. It doesn't load your spine as badly as a high bar back squat would. Its biomechanically very suitable for the human body and teaches you how to really lift with your hips and hamstrings and quads.
Here's what the guys at Westside say
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The Zercher squat. Ed Zercher invented this exercise years ago. I was first intrigued after reading about Robert Barnett doing the Zercher lift, where one squatted down and hooked the elbows under the bar and stood up. Mr. Barnett was capable of doing 5 reps off the floor with 395. His body weight was 165 and he could deadlift 675. He did this around 1966. After getting out of the army in 1969, I started doing Zercher squats off the floor. My best was 320, and I made a 670 deadlift in 1973 at 181. When I moved up to 198, I couldn't lift the bar off the floor because I had become too thick around the waist. I started doing a Zercher squat. I would lift the bar, which was on a low rack pin, in my elbows and go as low as possible. I used two versions:
One was to lower the bar until it sat on my knees. The second was to lower the bar out over my knees as low as possible, then drop my hips as low as I could to stretch the lower back and then stand up. With this method, I made 500 at an all-star wrestling convention. At the time I made an official 710 deadlift at 198. This was around 1978. I tore my right bicep almost completely off at the 1979 USPF Senior Nationals. After that, I could no longer hold the bar in my elbows with heavy weights.
In fact, they like it so much, they've invented an apparatus where you can place the bar at the midsection position, while hooking the apparatus to your shoulders. It really teaches you to keep your back straight to reduce pressure and torque at the hip angle.

its been a while but thx pizzaboy on Zercher squat. unload on the bench press rack is a b**** though.