If you do decide after reading all the comments on here, that you do want to make a will, but don't have the funds to pay for it, there are various charities that offer to write wills for free in return for you leaving them a gift in your will. Macmillan is one such example, but there are lots of others.
https://www.macmillan.org.uk/donate/gifts-in-wills/free-will-service
You could write the will to appoint whichever child you feel would be best placed to sort out whatever needs sorting as your executor. You could leave the charity a gift of say £200 in your will. (I appreciate you don't have that now, but things might change before you die, as hopefully it won't be for a long time yet). If you don't have £200 to leave in your estate before you die, the charity won't receive the donation (unless your children are well enough off and generous enough to donate it themselves in your memory). The rest of your estate, you can leave to be divided equally between all of your children. (Even though you don't think there will be anything to leave).
You say you don't want a funeral, so you need to decide what you want your children to do with your body when you die. Would they be willing to club together to pay for a direct cremation? This could still cost a couple of thousand pounds). If you don't want to pass this burden on to them, you ought to see what bills you can cut back on to invest the money in an insurance policy to cover the cost of an insurance policy. Perhaps if you have Netflix or Spotify or anything, cancel that to save your children from worrying about the cost of disposing of your body. There are pauper's funerals paid for by the council for people that die with no assets, but only if the next of kin have no assets either, so in your case, your husband or children would be expected to pay.