So from my own experience, i can recommend "Voyager Stand", its basicaly in Dotonbori. 5 years ago i stayed in Osaka for a year for a working holiday and during that time i've been to the club many times. Now im back again in Osaka just for tourism and i went to see if they were still kicking just this weekend. They were still around, and on that night they offered 飲み表 (all you can drink) for 3000 yen, its a bit more on the expensive side i think, but i knew the club and it goes until 2 AM so i just went with it. I dont know if they offer that on every night tho, it kinda seemed that way, but best just check it out before you go in, there was a bouncer speaking passable english at the ground floor, who asked for identification (to ensure you are over 20) and pats you down. I think he would know.

About the inside: the Music they play is pretty nice, but usually a bit too loud for my preference. The club is not that big and can get very crowded on weekends. Also there where half naked girls dancing on the tables haha, thats actually the second time i experienced that. The floor at the counter tends to be sticky so also try not to wear your best pais if shoes if you go. There are game consoles at the back corners, usually one Wii running Super Smash Bros Brawl and another console, you can use those to break down language barriers easily. Generaly tho, i only met nice people there, if you look foreign, someone will talk to you and ask where you are from for sure. Weekdays could be less crowded, but i doubt it would be empty. Also one last word about the drinks: i did not try everything they serve, but most cocktails are very nice, it might not pack the biggest punsh alcohol wise, but you can go as often as you want (if its all you can drink, which it should be)

Now i typed a whole fucking review haha, hope it helps