Hello, not an expert/lawyer and even if you want to make a very simple will it would be worth making the investment in getting a solicitor/professional will maker to draw up your wills just to make certain everything is properly done and you can relax knowing it's all watertight? It shouldn't be hugely expensive...
Re your questions, on the inheritance from your parents point, I don't think you can leave something you don't yet possess to someone else, but I guess it depends on whether you want to do something on the lines of leaving everything you own at the time of your death to the other person (in which case that would usually include the inherited property assuming you were in possession of it at the time of your death, unless there are any complications in how your parents left the property to you e.g. in a trust), or would you be wanting to do something different with the inherited property to the rest of your possessions? Also I guess since you are not married you may need to consider the value of the (potentially) inherited property, will it take your estate's total value over the inheritance tax threshold? If so this could be an issue for the surviving partner and something to discuss with the solicitor. You may want to consider ensuring you have adequate life insurance/savings to cover the tax that will be due (as well as the additional costs of rearing your son etc) - or of course you could get married which would (a) mean no tax due on the estate if you leave it all to him and (b) would resolve some of your NOK concerns, but I'm assuming it's a considered/fixed decision not to get married for other reasons?
Other things to think about/include, assuming a untimely/relatively young death, what are your and your partner's views on remarriage and 'protecting' your assets including the possible inheritance of your parents property for your son? There are lots of threads on this on Legal Matters if you have a search, there are some strong views (!), some people are very much of the opinion that assets should go to the surviving partner absolutely and without strings, even though this ultimately means they can then choose what happens to the assets, it can end up being divided with a future spouse/future half-siblings/step children, or they can even choose to disinherit the child entirely (well subject to the fairly minimal protections afforded by UK law). So some people feel it's important to 'protect' the assets for the children of the marriage/partnership by utilizing life interests/trusts, even though this can tie the hands of the surviving partner to some extent... again something to discuss between you both and with the solicitor.
On the burial arrangements and life support point, funeral arrangements are basically down to the person named as executor in the will (doesn't necessarily have to be their spouse/nearest relative, you can choose who you like), so assuming you name each other as executors and make your wishes clear you should be fairly 'safe' on that point (assuming you trust your partner to follow through and your wishes are reasonably achievable, not wanting to be blasted into space or similar 
). Medical decisions are slightly more tricky, in the UK these decisions including about life support are ultimately down to doctors and an assessment of the best interests of the patient (assuming the patient isn't able to speak for themselves), but of course the person's family is involved and consulted and their agreement to any decisions sought. In general when doing this the doctors, or in the event of a dispute, the court will 'count' the person's life partner above/alongside parents/siblings, whether or not they are married but of course conflict can happen all the same and be very very stressful. I think a letter of intent indicating the person's wishes in that scenario would be very helpful (I don't think this is totally legally binding or formally part of the will but you can attach a witnessed/notarised 'statement of wishes' or similar). You could also potentially execute LPAs for health/medical matters in favour of each other, although people usually only do this when older or already sick as it lasts the whole of your life unless rescinded, so obviously in the event of a break-up it would be added complications - but if you are really concerned about interference from his family that would be the most legally tight way to make sure you are the person in the driving seat...