Anchor to last session
Your log is the answer. Load the same weight you used before, and only add load once you have earned it by hitting your target reps across every work set.
Base it on your last session: hit the top of your rep range on all sets, add the smallest jump; miss, repeat the weight.
Pick a rep range like 6 to 10, then use double progression. If you got all sets to the top number last time, add 2.5kg for upper body or 5kg for lower body. If you fell short, repeat the same weight and try to add reps. The right working weight leaves you 1 to 3 reps from failure on your last set.
Your log is the answer. Load the same weight you used before, and only add load once you have earned it by hitting your target reps across every work set.
Say your range is 8 to 12. Start at a weight you get 8 with, grind up to 12 over weeks, then jump up and drop back to 8. This keeps overload steady without guessing.
A good working weight lets your last set finish with 1 to 3 reps left in the tank. If you could do 6 more, the weight is too light; if you fail early, it is too heavy.
Base it on your last session: hit the top of your rep range on all sets, add the smallest jump; miss, repeat the weight.