Can anyone recommend a decent brand for DIY hair trimming? There seem to
be so many on the market from a few pounds upwards. Preferably one which
doesn't need the blades oiling.

I have very thick hair and tend to cause most clippers to burst into flames.
For me, I go for a model with

(a) ceramic blades that don't need lubrication and cut more efficiently
(b) genuine mains motor which has significantly greater torque than the LV
motors used in battery and mains-rechargable types.

Almost all ceramic bladed clippers are also mains rechargeable. This is
because it is hard to make the weedy mains rechargeables work without the
efficient blades, so the two features tend to go hand in hand.

However, there are a few models combining ceramic and true mains motors and
they are worth seeking out. I got my last pair from Argos (made by Babyliss)
after I reduced my Wahl set (mains/steel) to sounding like a bag of bolts in
a washing machine. However, I note they no longer stock it.

Christian.