Blue acaras are surprisingly mellow for cichlids of their size and I'd watch the salvini with them. Acaras are also slower and I think would have trouble avoiding the convicts and salvini as they grow. Firemouths are a possibility but I'd either get 1 or three as opposed to two, most cichlids are highly aggressive to others of the same species and the larger might eventually be nasty to the smaller. Firemouths tend to be mellower than convicts and might be picked on so I think your best bet is to go with a male firemouth, as they're a little tougher. They tend to bluff with their aggression, so a bigger male would have an easier time protecting himself from highly overconfident convicts. Another option would be a female Jack Dempsey, which are pretty common and my female is super mellow and lives with an angelfish. I once had to move out my male firemouth who lived with my JD for being a huge jerk to my Electric blue acara, so once again watch the acaras. Another non-cichlid option could be a red tailed black shark, who tend to be pretty spicy and hold their own against cichlids being fast and aggressive on their own, as well as making a good addition to the cleanup crew. They are known to and in my experience have antagonized firemouths though. Pictus catfish also prefer to school and probably would be more comfortable if you brought in a couple more. Keep in mind with cichlids, the more you add, the less aggression will be focused on one individual, and spread out over them all, so 6-8 should be fine for a 100g. Another option could be some pink convicts or marbled convicts, as they would have the same temperament as yours but add more variety. Female convicts only get 2-3" as opposed to larger males, so you can have several without really affecting the bio-load.