On the subject of the lower headset bearing, mine's knackered too as many of you know. OEM fitment is an FSA bearing, so not a Decathlon corner cutting thing per se but anyway, looking into it, the bearing is fairly generic & fitted on loads of bikes- standards innit. If you wanted to replace, you need a 51.8mm 36/45 in either 7.5mm or 8mm depth, 40mm internal.
If you don't know already, 36/45 refers to the external angle of outer bearing I.e. it's 36 degrees then 45 degrees. Everywhere I look, they're about £16 & I guess fitting a shorty mud guard to the fork arch will go some way to protecting it from the worst of the dirt & water.