Would cross training wrestling or bjj not mma alongside my silat cimande harm my silat training, or should I just stick with the Silat purely?
wrestling might provide you better control work. BJJ classes vary in standup quality but have great ground work
Since you are in the UK and already into cimande, I suggest that you find the harimau silat group that is a recognized group under Pendekar Richard DeBordes.. The group is based in the UK region.. Google Harimau silat and Richard Debordes, it should send you into the right direction
If you want to study BJJ, then do it. Don't be afraid it would ruin Silat. It might affect but trust me, it doesn't matter. I know, here , in Indonesia, a master have learnt hard style first and then soft style. Then when he demonstrate the hard style, it has been changed. It doesn't matter. People understand.