Northener,
The main point as you mention is that you do not need a Professional Trustee (PT) therefore nobody is required to do this job. The main reason for a member of a SSAS to continue with a PT is because HMRC is said to see schemes with a PT as 'lower risk', however, if everything is kept above board then I fail to see how this can impact you. PTs are also appointed when there are relationship issues between scheme members etc and having a 'neutral' trustee involved can add an extra level of security as will be required to sign on any investments and money movements.
It is possible you could arrange for a company to administer the scheme without being PT, appoint them as Scheme Administrator and arrange for them to do all the reporting etc… As I said you needn't pay for scheme accounts. The problem with this would be that many providers insist on certain things for example the accounts (as it makes their life easier) but there are a couple who are very flexible in their service and don’t charge you to transfer your scheme to them.
The other option is of course to administer the scheme yourself, which I wouldn't take lightly!! I have had many a scheme transfer to me because the members believed they could manage it themselves but had missed years of returns, failed to report, had incorrect trustees named on investments and incurred large penalties that exceeded the cost of someone else to administer it in the first place!!!
You ask what the difference between a Pensions Solicitor and Pension Trustee is, to keep it simple, a Pensions Solicitor is a Solicitor that specialises in pensions law, and a Pension Trustee is the Trustee of a Pension that will jointly make decisions with the member trustees.
I think what you meant to ask was what is the difference between a Pensions Solicitor and a SSAS Provider, apart from one being more expensive than the other a SSAS Provider deals with all areas of Administration including the drafting of trust deeds , purchasing of investments and providing valuations, a Pensions Solicitor will usually be involved with the legal documents such as deeds of appointment, removal and amendment or any legal situations that may arise within the scheme.