@Rayster: I can only think of one BL isekai that's played straight (i.e. written with the tropes from the current fad of isekai in mind), and it's quite raunchy vapid yaoi stuff, and I can't actually recommend it as such:
Trip Lovers. Also, it's both short and not terribly memorable.
(If this is really what you want out of life though, you might enjoy it. I know I did, but possibly for the wrong reasons, like laughing at the inherent comedic justice of BL getting its turn at the wheel of rather inappropriate isekai sexual fantasies).
There's probably a very small but respectable set of old stuff from the bygone days of the
Ichiraci magazine (which was once upon a time had a really good run of adventure/fantasy/sci-fi/etc shounen-ai) that would probably fit the textbook definition of "isekai"; Morimoto Shuu's
Jinjuu Houretsuden comes to mind off the top of my head (I never finished reading it, but what I recall from what I read seemed quite good—maybe a faint hair on the hammy dramatic side sometimes as all such things were back then, though not at all the worst offender, and with enough good points to make up for it).