I'm very sorry for your loss.
It may be sensible not to rush into getting more rats immediately, just in case your other lad died of something acutely infectious. What looks like sudden respiratory distress is often a heart attack or stroke, though, especially if death follows soon after. And you only need to wait a couple weeks to make sure Coolio hasn't caught anything that would harm any new rats, so you can start searching for new friends for him now, especially as it can take a little while to find rats that fit your situation.
Adult male rats generally accept young males more readily; around 10 weeks is ideal as much older than that and they start to smell more adult, but much younger than that and they're not big enough to stand up for themselves in an argument. Rats that young will need similar age company though, so you'd need to get a pair. You could also get an older male rat, or an older pair/small group of males; adult male intros are (as I understand it) a little bit more tricky, but if anyone's causing problems, neutering usually sorts it out, or getting them the hormonal implant as an alternative to neutering.
Poo-shoveller to: Calyn (NLA32); Zephyr Nyahir; Zephyr Zymandis; Zephyr Blasto.
Fondly remembering: Zephyr Mick Jagger "Edgeworth"; Din (NLA28); Zephyr Donovan "Phoenix"; Xeltan; Lita (NLA32); Lia (NLA28); Zephyr Delanynder (NLA28); Falere (NLA36); Mirala (NLA36); Zephyr Opold; Rila.
