For trousers, you can’t go wrong with a pair of M43, field grey woollen Keilhosen, which are designed to be worn with your ankle boots and gaiters, these can be got from Spearhead Militaria for around £30. http://stores.ebay.com.sg/Spearhead-Miliaria.

The other option you have is buy yourself a pair of oak A or “eichentarn” US BDU trousers, you can pick these up for around £12, it’s a cheaper option, but you need to cut off the modern side pockets with a kraft knife to get the right effect. They have a reinforced seat and reinforced knee area, and are very similar to the late war panzerhosen, but a fraction of the cost. These BDU trousers are quite common and usually available on e-bay from moleskin-militaria or the local army and navy surplus.