if its size youre after then ideally you want to lpwer the reps and raise the weight. say 4 reps and sets of 5. without seeing you train its hard to say a specific starting weight, best thing to do is go see a personal trainer or a free trial at a gym, safest way to avoid injury imo.
and before you goloading the weights up, make sure you do plenty of stretching exercises and warm up reps, these will be minimal weight or just the bar weight for warm up reps.