I used to write wills for a living. The advice which I've given many times on here is to get hold of a copy of this book:
Amazon.co.uk User Recommendation
It's in most public libraries. (It won't matter if it's an older edition; while the law relating to intestacy has changed recently, the stuff about writing wills still remains valid). Read through it and prepare your own will, simply typed onto blank paper.
If you're completely happy that you've got everything covered, sign it in the presence of two witnesses (who must not be beneficiaries under your will) and get them to sign as witnesses. (Then ensure that you've told your sons where your will is kept!). If you're not 100% happy with what you've drafted, seek further advice.
You can appoint your sons as executors, so there's no need to involve a solicitor at any stage. In the (probably unlikely) event that your sons decided that they needed legal help they could still appoint their own solicitor.