cross-harp

For second position use a C harp to play in G, use a G harp to play in D, use an A harp to play in E, use a D harp to play in A, etc. There are many charts on the internet.
Lee Oskar major diatonics are labeled in first and second position. On a C harp one end says 1st C and the other end says 2nd G.
Second is the way to play blues. If you also want to play melody in second you might want to look into Country tuned diatonics. That is what Charlie McCoy and Buddy Greene play. Only one note is changed. On a C harp draw 5 is an F. In the key of G all Fs are sharp so when playing in G on a C harp the draw 5 will be flat. That sounds bluesy but doesn't follow the melody. Country tuned harps raise draw 5 half a step. They are designed to play in second.
For bending on diatonics I like Hohner Special 20 or Lee Oskar. Special 20 can be purchased in Country tuning.
You can turn any standard harp into a Country tuned by tuning up draw 5. That's how I got mine.