I'd suggest the most obvious buy would be a standard Ferguson 2 furrow plough. You should pick up a decent one for £200 and if you decide its not for you , you will get your money back when you sell it. Will complement your 135 perfectly.
Can't argue with stufe35 in the round: a decent Ferguson plough would be ideal for your 135, but the problem will be finding one locally so that you can look-over before buying. I couldn't find one in the SW when I was looking - they were all up North ! (Actually, I couldn't find any old Ferguson plough - or other contemporary brand - advertised as usable 'out of the box' for just £200: I reckon one needs to pay more than that for a goodun.)
Obviously ploughs take a bit of a hammering: best you check web resources that offer help with identifying potential problems with the old ones - regrets I haven't saved any relevant web links.
I think it was oor wullie who advised that ploughing is easy, but not easy to do well. I can vouch for that and I can also vouch for the fact that it is very difficult to turn a good furrow with dense grass cover. AND setting up a plough properly on your tractor in the first place is also not easy for a novice !
Next, you will need some sort of harrow to break up the plough furrows idc !
If you are re-seeding for pasture, it won't matter that you have brought a whole load of existing seeds up to the surface, but it will matter if you want to create areas for sowing fodder/other crops. If the latter, you will need to keep at it for a while (ploughing/harrowing) to knock-back any new grass growth (or you
will need to use herbicide).
In the end, I bought what I believe to be a Polish-built 2 furrow plough from machinerysalesEU Ltd: obviously I put it through it's paces immediately and, as indicated above, soon learned that set-up and ploughing is not easy. Unfortunately, for a whole load of reasons last year, I had to put skilling-up to one side and I haven't yet, for another load of reasons this year, attempted a meaningful retry: therefore I cannot offer any useful user comment on the msEU plough. What I do know though is that I would have gone for a good old Ferguson (or equivalent) if I could have found one !!
I have a few other thoughts, but gotta go right now.