Sorry I am not that expert, Robusta (?) Beans are know to be stronger than most, but tend to be bitter. More than one per day...definitely addictive. Really strong caffeine beans are very bitter and you have to add something to make it palatable.
Easiest way to get a stronger coffee... use more beans, ie find one you like and double the your usual dose. Choose a machine with a big 'hopper' as it were. Or Mokka (?), a percolator to use on a hob, or solid fuel stove...is also good to produce a strong brew.
Last Christmas a friend got me some whisky flavoured ground coffee...Vanilla us also nice.
Robusta is the reason chocolate was added to cappuccino, to balance the bitterness. It was (still is?) cheaper than Arabica beans. These days I just use a nespresso machine and 2 pods per cup. Lidls intenso is pretty good. Got sick of waiting for Nespresso deliveries a long time ago