Hi notnamed - this is my 2nd attempt tonight - typed a really long reply and lost it aaaargh! So will try again.
Firstly you would be able to be considered as a foster carer if you are single. There are different types of fostering: short term (anything from 2 day to 2 yrs +) permanent, as its name suggests, and respite care which means taking a child from a foster carer who wants a break, (maybe for 2 weekends a month or whatever arrangement is worked out) and some LAs have schemes where respite carers take children for a short period from parents who are struggling to cope.
The thing with short term is there is no guarantee that you will be kept in work for 52 weeks of the year. With permanent fostering there is more security, in that you will be paid as long as the child is with you, BUT these placements can break down and if this happens and the child has to move the money is stopped.
Being a single carer will be something of a problem because social workers trying to place a child will almost always go for a couple. The other thing is that the foster child will need to be younger than your own child,so as he/she does not have to compete with younger children and it is important that your son retains his position as the oldest in the family. There needs to be at least a 2 year age gap and you would therefore be looking at a child of 5 or under. This would raise another problem if you were thinking of permanent fostering because the care plan for a child of 5 and under will be adoption. However there is still a shortage of adoptors for children of 5 and over, and sometimes under 5, dependent upon the child's circumstancs.
You will know I am sure that all children removed from parents will have been abused and/or neglected and will have to a greater or lesser extent behavioural problems, which manifest themselves in a variety of ways. All will by definition have insecure attachment with birth parents, meaning that they have learned that adults are not to be trusted and it is hard work to reverse this, but it can be done.
As for finance - of course you need to be sure that you are financially stable. In a sense permanent fostering would be best because the fostering allowance is mandatory and the adoption allowance is means tested and is discretionary and is reviewed annually and can be altered or even stopped especially as all LAs are now totally cash strapped thanks to the coalition govt.
However this leads to another problem because if you apply to permanently foster a child of 5 or under you will undoubtedly be asked why you are not thinking of adoption. You could be honest and say that you know adoption allowances are discretionary etc and you will probably be told that it wouldn't be a problem with allowances, but it could be at some point in the future.
The other thing is that sometimes adoptive homes are sought for children of 5 and under and cannot be found and then sws will be looking for a permanent foster carer, by which time the child could be 6 or 7 or older and of course your own son would be older.
Re your accommodation - this would be a problem because a fostered or adopted child will need his/her own room and it isn't fair in any event to expect your son to share his room. Are you sure your son is tough enough to cope with sharing you and having a young child around who may have difficult behaviour. And NO the LA will not help with housing costs as they are cash strapped - maybe if you were considering a sibling group of 4 or 5 they made see it as a cost effective way of placing these children.
I know it all sounds very mercenary but that is the reality I'm afraid. As far as I can see the bottom line is that you would be accepted as a permanent foster carer for a child who was waiting for adoption and this was not forthcoming and no couples were interested in permanently fostering this hypothetical child.
The other thing is that I would be very careful about going to Barnardoes or any voluntary organisation. They will assess you much quicker than the LA because they are very well resourced BUT they don't have children to place - only the LA have children to place. The voluntaries therefore recruit families and have to try to "sell" them to the LA for a particular child, and charge very high fees for the sale. LAs obviously have a preference to use their own "in-house" prospective foster carers and addoptors because it is the cheapest option. The next cheapest option is for an inter-agency placement (placing the child with another LA) the last resort is a voluntary because of the costs involved.
You could go along to Barnardoes and ask their views on your situation and they will probably be encouraging, but hopefully will be honest with you about 5's and unders needing adoption. It would be a good idea to ask how many children of this age (or slightly older say 6 or 7( they had placed for permanent fostering in the past 2 years - I would be interested in their response.
Also you can approach your LA (or any LA) and all follow the same legislation but may well differ in their response. Don't be reluctant to ask as much as you need to know - that's what they are there for!
Finally if you look on the following sites you will get more info: "British Agencies for Fostering & Adoption (BAAF) "Adoption UK" and "Fostering Networks"
Hope I haven't confused you too much.
Be interested to hear how you get on.
I am aware I have looked at worse case scenarios but that is often the best way and then if things turn our better, that is a bonus.