It doesn't matter what "company" you book with, you'll be on the same boat/s as everyone else. A package deal should cost around 1600 baht including transport to Chiang Khong , overnight at a guesthouse (probably Namkhong Guesthouse) with dinner, breakfast and a lunchbox thrown in, plus all transfers and of course the slow boat ticket (costs about 800 baht independently). Package doesn't include Laos visa ($30-42) and guesthouse the 2nd night in Pakbeng. Pretty sure Aya Tour offers this deal but it might involve an overnight van to Chiang Khong (no sleep) otherwise get a bus/van back to Chiang Mai Arcade bus station and grab a bus to Chiang Khong either direct or via Chiang Rai. You can hook up the slow boat independently, after arriving in Chiang Khong get across to Huay Xai on the Laos side, get a visa etc stay 1 night and walk to the slow boat ramp 1km north of town center and buy ticket directly should be about 200,000 kip, boat leaves about 11am try to sit near the front (less noise) bring something soft to sit/lie on and extra food/drink (available at restaurants right next to the boat). Tons of available rooms in Pakbeng, ignore touts trying to pre-book you a room for twice the price. Enjoy.