Could someone recommend which blades I should try now? I have fairly sensitive skin, but my hair is extremely dry and coarse. Great combo, obviously.
IMHO, ditch the Merkur blade, they're not great.
I've found for me that the Personna red pack is pretty good, very smooth, hardly feels like it's doing anything, especially good when teamed up with Truefitt & Hill Sandalwood cream. I find Derby are pretty good and work well with any soap or cream, Israeli Personna's are ok, but Gillette 7o'clock green feel like they're pulling and tugging rather than slicing. It's been a while since I used any others I wouldn't like to comment.
For you, the Personna red pack blades might get dull to quickly, try Derby maybe. They seem to be a pretty good all-rounder for lots of hair types.
Also, different blades feel and work differently with different soaps and creams, and each blade make has its own nuances you need to adapt to. And of course the hardness and temperature of the water makes a difference but I'm sure you already know that.
Stick with one make of blade for a while and try out different techniques till you learn the blades. I kept making the mistake of working through the samplers too quickly and not learning the blades. Now I can put in any blade and get a great result (except the 7o'clock greens but even that is better than a Mach3)
(I use the Merkur 38C, Kent BK4 brush and any one of various Truefitt & Hill, Trumper, Taylor of Old Bond Street soaps and creams, depends what takes my fancy at the time.)