Yeah SV J is great for earning. All booking classes earn 150% at least, if I am right I class the cheapest followed by D. D is a bit more flexible with changes. You should be able to find the class via manage my booking and it should be also on any ticket you have got. TUN-BKK gives you 108 XP and if you are plat due to the plat bonus well above 30k miles (say 300 Euro worth).

And yes, ITA in J becomes very interesting for intra-Europe trips. If your employer only pays Y, arrange/agree to top-up yourself to J and for a few 100 Euro extra you may have 60 XP instead of 10-20.....