Interview tomorrow...how do I spin being let go or laid off from my previous sales job?

Hi guys,

I've been unemployed for about a month and a half now. I took some of that time to relax and reflect, then started applying for new jobs about 3 weeks ago. I have my first interview tomorrow at a company I'd really like to work for. I'm just trying to figure out how I can best answer the question of "why did you leave" or "why were you let go".

Basically I had been at my last company(high-end software sales from $10k-$50k) for about 3.5 years in software sales. It was a very bumpy road in terms of cashflow in the beginning, and they had problems paying us(only started with 3 of us, myself and two other sales people) on time in the beginning. One of the guys had been there for about 2 years before myself and the other guy who started with me. About 6 months in, he was let go after a sales slump, along with the only marketing person we had. Then we hit a rough period and we weren't paid for a few months and morale was a bit low. All the while we would make sales here and there, but the process for customer acquisition wasn't the best(only cold calling), so it wasn't exactly easy going. At the two year point, the other sales guy left/was let go, and then it was just myself.

It was a challenging time, but I was able to close some deals and make some steady progress. We added a few min wage sales support workers to help with cold calling and booking appointments for my presentations, but it was still somewhat slow and we had turnover in that area too. We did manage to have one girl stay with us, so it was just myself and her for another year. We had a nice influx of cash from a company that I had been calling(over a few years) who ended up having an urgent need for our service and ended up calling in at a time that I was away on vacation, so the CEO kept that lead for himself. I let that go though...he insisted that he made the call, but that didn't really jive with me. Water under the bridge.

Anyway, so we ended up hiring another sales person, and later a sales support person and continued on. I made a few sales in that time frame, but everyone else was still getting up to speed and things were still slow. Then we lost a pretty big customer and it looked like things were starting to get tight again. So then, one day my boss called me in, at the end of the day and explained that they had to let me go or lay me off. The reason was that things were tight, I was the most expensive employee, and I had been there the longest, through the crappy time, so they felt that they could start fresh with the less expensive, fresh staff who hadn't been there as long as me. It wasn't a total shock since we've been down this road before. But it was also a good time for me to have a change since I wasn't really happy in that job. I had started looking to leave about 6 months earlier, but got distracted while having to look after my elderly parents. They didn't really have the drive and strategy to make things happen. It was a very laid back environment(CEO didnt even some in until 11 most days) and we were a tiny company (5 of us in the office). They refused to take action on any other methods for acquiring new customers(eg. digital marketing) and relied solely on cold-calls, so as soon as calls and leads slumped, so did booking, presentations, free trials, and sales. It was still a good experience overall where I picked up additional sales and presentation skills selling high-end software. We are on great terms and they(CEO and partner CTO) will provide me with any positive reference I need.

Sorry, this got kinda long. All of this to say, that I don't know how best to explain this to the hiring manager I'll be speaking with tomorrow. How can I frame it so that it comes off in the most positive light? My old boss would pretty much say whatever I wanted him to say, if he acts as a reference, but I'm not trying to lie about it...just spin it so that it comes off better. Any suggestions?