The Marina 10 watt is great as a pre-set one as it'll heat the water well. It keeps my tanks at a constant 8o-81 degree's.
I recommend feeding him New Life Spectrum. It is a bang for your buck but it'll keep him happy through out his entire life. I use the small fish formula because my betta's both have rather small mouths and spit out anything that's too big including flakes. Bettamin is a good additive to their diet because it contains brine shrimp. I wouldnt feed it too often as their only meal. Amp up his food schedule too as they need daily feedings and one day fasting. Two feedings a day should suffice with pellets. I heard eposm salt also helps with the bloating problem...Someone correct me if I'm wrong.
Also: Blazer-san your not giving out very good advice except for the minor stuff like water additives. Everything else is either wrong or the last resort.
OP I hope your betta feels better.