There are different types of measurement for attitude. You may want to take a look at Ajzen's "Attitudes, Personality and Behavior".
You may also take a look at papers that worked on Theory of Planned Behavior and implement their measures of attitude. As a simple instruction, I suggest to ask the respondents idea about the eco friendly product and give them a 7 point Likert-scale from extremely likable to not at all likable. If you need multiple questions, ask them the same question with following adjectives as the answer (pleasant/unpleasant), (harmful/beneficial), (good/bad) and (awful/nice).
Like Hosein indicated you can ask consumers/ respondents several questions in a N-ponit Likert scale concerning eco friendly production and product. After getting the responses from consumers, you can use principal component analysis to analyse the individual questions you asked and come out with significant components indicated by the factor analysis using the eigen values. When you obtain these components you can include them as variables in a preference and willingness to pay for the particular product you are interested in. The principal component analysis will give you the percentage variations explained by the components retained which gives better understanding of consumer behaviour than just using socioeconomic factors
This paper is not exactly on "attitude towards eco-friendly products" but, given its focus on green products, maybe it can be useful:
Romani S., Grappi S., Bagozzi R.P. (2014) - Corporate socially responsible initiatives and their effects on consumption of green products - JOURNAL OF BUSINESS ETHICS Online first: 26 November 2014 (http://link.springer.com/article/10.1007/s10551-014-2485-0)
This can be measured by following several techniques. Please, find for example my research paper entitled "Evaluation of New Packaging Formats for Dry-Cured Meat Products Using Conjoint Analysis: An Application to Dry-Cured Iberian Ham."on my research gate profile.
We have published many papers on consumers' behaviour towards orgnanic food.
If you have any doubt, please do not hesitate to contact me.
Attitudes can be determined by asking three major aspects, awareness, feelings & behavior. You may also refer to Tri component model in CB. A well designed & reliable scale will be of great help. Good Luck.
I conducted research on understanding psychological factors like attitude, desire, intension and perception by developing different measures on a 5 point Lijert scale